Add MemberGroup descriptions (System.T)

[gewarren]

Contributes to #12626.

[Copilot]

Pull request overview

This PR addresses #12626 by adding missing <MemberGroup> entries (with <summary> descriptions) for overloaded members across a broad set of .NET API reference ECMAXML files, improving the grouped-member documentation experience in generated docs.

Changes:

• Added <MemberGroup> nodes with summaries for many overload sets (constructors, Equals/CopyTo, async APIs, etc.).
• Replaced some “To be added.” placeholders with meaningful summaries (for example, CodePagesEncodingProvider.GetEncoding).
• Updated System.Text.Unicode.Utf8 to include a TryWrite member group (and reformatted the file in the diff output).

Reviewed changes

Copilot reviewed 79 out of 79 changed files in this pull request and generated 16 comments.

Show a summary per file

File	Description
xml/System.Transactions/TransactionOptions.xml	Add Equals member group summary.
xml/System.Threading/ThreadPool.xml	Add UnsafeQueueUserWorkItem member group summary.
xml/System.Threading/ThreadingAclExtensions.xml	Add member group summaries (Get/SetAccessControl).
xml/System.Threading/Thread.xml	Add UnsafeStart member group summary.
xml/System.Threading/SpinWait.xml	Add SpinOnce member group summary.
xml/System.Threading/PeriodicTimer.xml	Add constructor member group summary.
xml/System.Threading/Lock.xml	Add TryEnter member group summary.
xml/System.Threading/Interlocked.xml	Add And, Or, Read member group summaries.
xml/System.Threading/CancellationToken.xml	Add UnsafeRegister member group summary.
xml/System.Threading.Tasks/ValueTask`1.xml	Add ctor + Equals member group summaries.
xml/System.Threading.Tasks/ValueTask.xml	Add ctor + Equals member group summaries.
xml/System.Threading.Tasks/TaskFactory`1.xml	Add ContinueWhen* / FromAsync* member groups.
xml/System.Threading.Tasks/TaskFactory.xml	Add ContinueWhen* / FromAsync* / StartNew member groups.
xml/System.Threading.Tasks/TaskCompletionSource`1.xml	Add SetCanceled member group summary.
xml/System.Threading.Tasks/TaskCompletionSource.xml	Add ctor + Set* / TrySet* member groups.
xml/System.Threading.Tasks/Task`1.xml	Add ConfigureAwait / ContinueWith / WaitAsync member groups.
xml/System.Threading.Tasks/Task.xml	Add multiple member groups (ConfigureAwait, Run, WhenAll/Any, etc.).
xml/System.Threading.Tasks/Parallel.xml	Add For* / ForEach* member groups.
xml/System.Threading.Tasks.Dataflow/WriteOnceBlock`1.xml	Add constructor member group summary.
xml/System.Threading.Tasks.Dataflow/TransformManyBlock`2.xml	Add constructor member group summary.
xml/System.Threading.Tasks.Dataflow/TransformBlock`2.xml	Add constructor member group summary.
xml/System.Threading.Tasks.Dataflow/JoinBlock`3.xml	Add constructor member group summary.
xml/System.Threading.Tasks.Dataflow/JoinBlock`2.xml	Add constructor member group summary.
xml/System.Threading.Tasks.Dataflow/DataflowMessageHeader.xml	Add Equals member group summary.
xml/System.Threading.Tasks.Dataflow/DataflowBlock.xml	Add Choose/LinkTo/Receive*/SendAsync member groups.
xml/System.Threading.Tasks.Dataflow/BufferBlock`1.xml	Add constructor member group summary.
xml/System.Threading.Tasks.Dataflow/BroadcastBlock`1.xml	Add constructor member group summary.
xml/System.Threading.Tasks.Dataflow/BatchedJoinBlock`3.xml	Add constructor member group summary.
xml/System.Threading.Tasks.Dataflow/BatchedJoinBlock`2.xml	Add constructor member group summary.
xml/System.Threading.Tasks.Dataflow/BatchBlock`1.xml	Add constructor member group summary.
xml/System.Threading.Tasks.Dataflow/ActionBlock`1.xml	Add constructor member group summary.
xml/System.Threading.RateLimiting/RateLimitLease.xml	Add Dispose member group summary.
xml/System.Threading.RateLimiting/RateLimiter.xml	Add Dispose member group summary.
xml/System.Threading.RateLimiting/PartitionedRateLimiter`1.xml	Add Dispose member group summary.
xml/System.Threading.Channels/ChannelClosedException.xml	Add constructor member group summary.
xml/System.Threading.Channels/Channel`2.xml	Add op_Implicit member group summary.
xml/System.Threading.Channels/Channel.xml	Add Create* member group summaries.
xml/System.Text/StringBuilder+AppendInterpolatedStringHandler.xml	Add ctor + AppendFormatted* member groups.
xml/System.Text/StringBuilder.xml	Add AppendJoin*/CopyTo/Equals member groups.
xml/System.Text/Rune.xml	Add ctor/Equals/IsValid/etc. member group summaries.
xml/System.Text/RedactionStringBuilderExtensions.xml	Add AppendRedacted member group summary.
xml/System.Text/EncodingExtensions.xml	Add Convert/GetBytes/GetChars member groups.
xml/System.Text/CodePagesEncodingProvider.xml	Replace placeholder summary for GetEncoding group.
xml/System.Text/Ascii.xml	Add multiple member group summaries (Equals, casing, Trim*, etc.).
xml/System.Text.Unicode/Utf8+TryWriteInterpolatedStringHandler.xml	Add ctor + AppendFormatted* member groups.
xml/System.Text.Unicode/Utf8.xml	Add TryWrite member group summary.
xml/System.Text.RegularExpressions/Regex.xml	Add Count / enumerate member group summaries.
xml/System.Text.RegularExpressions/MatchCollection.xml	Add CopyTo member group summary.
xml/System.Text.RegularExpressions/GroupCollection.xml	Add CopyTo member group summary.
xml/System.Text.RegularExpressions/GeneratedRegexAttribute.xml	Add ctor member group summary.
xml/System.Text.RegularExpressions/CaptureCollection.xml	Add CopyTo member group summary.
xml/System.Text.Json/Utf8JsonWriter.xml	Add ctor + write APIs member group summaries.
xml/System.Text.Json/Utf8JsonReader.xml	Add ctor + CopyString / ValueTextEquals member groups.
xml/System.Text.Json/JsonSerializerOptions.xml	Add ctor + MakeReadOnly member groups.
xml/System.Text.Json/JsonSerializer.xml	Add Serialize* / Deserialize* member group summaries.
xml/System.Text.Json/JsonProperty.xml	Add NameEquals member group summary.
xml/System.Text.Json/JsonException.xml	Add ctor member group summary.
xml/System.Text.Json/JsonEncodedText.xml	Add Encode / Equals member group summaries.
xml/System.Text.Json/JsonElement.xml	Add GetProperty / Parse / TryGetProperty / ValueEquals member groups.
xml/System.Text.Json/JsonDocument.xml	Add Parse member group summary.
xml/System.Text.Json.Serialization/JsonStringEnumConverter`1.xml	Add ctor member group summary.
xml/System.Text.Json.Serialization/JsonStringEnumConverter.xml	Add ctor member group summary.
xml/System.Text.Json.Serialization/JsonSourceGenerationOptionsAttribute.xml	Add ctor member group summary.
xml/System.Text.Json.Serialization/JsonNamingPolicyAttribute.xml	Add ctor member group summary.
xml/System.Text.Json.Serialization/JsonDerivedTypeAttribute.xml	Add ctor member group summary.
xml/System.Text.Json.Serialization/JsonConverterAttribute.xml	Add ctor member group summary.
xml/System.Text.Json.Serialization.Metadata/JsonTypeInfoResolver.xml	Add Combine member group summary.
xml/System.Text.Json.Serialization.Metadata/JsonMetadataServices.xml	Add GetNullableConverter member group summary.
xml/System.Text.Json.Serialization.Metadata/JsonDerivedType.xml	Add ctor member group summary.
xml/System.Text.Json.Schema/JsonSchemaExporter.xml	Add GetJsonSchemaAsNode member group summary.
xml/System.Text.Json.Nodes/JsonValue.xml	Add Create* member group summaries.
xml/System.Text.Json.Nodes/JsonObject.xml	Add ctor + mutation/query member group summaries.
xml/System.Text.Json.Nodes/JsonNode.xml	Add conversion + Parse member group summaries.
xml/System.Text.Json.Nodes/JsonArray.xml	Add ctor member group summary.
xml/System.Text.Encodings.Web/UrlEncoder.xml	Add Create member group summary.
xml/System.Text.Encodings.Web/TextEncoderSettings.xml	Add ctor member group summary.
xml/System.Text.Encodings.Web/TextEncoder.xml	Add Encode member group summary.
xml/System.Text.Encodings.Web/JavaScriptEncoder.xml	Add Create member group summary.
xml/System.Text.Encodings.Web/HtmlEncoder.xml	Add Create member group summary.