Fix VSTHRD110 firing in Expression-valued scenarios

[Copilot]

Summary

This PR fixes VSTHRD110 analyzer incorrectly firing when Task-valued lambdas are passed to methods expecting Expression<> parameters. In these scenarios, the lambda is converted to an expression tree (data structure) rather than being executed, so no warning should be shown.

Problem

When using libraries like Moq, VSTHRD110 would incorrectly fire on legitimate code:

using Moq;

var mock = new Mock<ILogger>();
mock.Verify(
    x => x.InfoAsync(It.IsAny<string>()), // VSTHRD110 incorrectly fires here
    Times.Never,
    "No Log should have been written");

public interface ILogger
{
    Task InfoAsync(string message);
}

The lambda x => x.InfoAsync(It.IsAny<string>()) is converted to an Expression<Func<ILogger, Task>> for inspection by Moq, not actually executed, so VSTHRD110 should not apply.

Solution

Added detection logic to AbstractVSTHRD110ObserveResultOfAsyncCallsAnalyzer that:

1. Checks if invocation is within a lambda: Walks up the operation tree to find containing IAnonymousFunctionOperation
2. Detects Expression<> conversion: Identifies when the lambda is converted to System.Linq.Expressions.Expression<T> via:
   • IConversionOperation (direct assignment: Expression<Func<T, Task>> expr = x => x.Method())
   • IArgumentOperation (method parameter: SomeMethod(x => x.Method()) where parameter is Expression<>)
3. Suppresses diagnostic: Skips VSTHRD110 when expression tree conversion is detected

Test Coverage

Added comprehensive test cases covering:

• ✅ Moq.Verify-like scenarios (mock.Verify(x => x.InfoAsync("test"), Times.Never))
• ✅ Direct assignment (Expression<Func<T, Task>> expr = x => x.InfoAsync("test"))
• ✅ Method parameters (SomeMethod(x => x.InfoAsync("test")) where parameter is Expression<>)
• ✅ Regression test ensuring normal Task calls still trigger VSTHRD110

Edge Cases Handled

• Intermediate operations like parentheses between lambda and conversion
• Generic Expression<> types with various Func signatures
• Other expression tree types in System.Linq.Expressions namespace

Fixes #1167.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• 1elvsblobprodwus2177.vsblob.vsassets.io
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