BigQuery: JSON writer does not function if table schema has fields with mixed-case names

[stephenjudkins]

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Environment details

1. Specify the API at the beginning of the title. For example, "BigQuery: ...").
   General, Core, and Other are also allowed as types
2. OS type and version: N/A
3. Java version: N/A
4. bigquerystorage version(s): 2.4.0 (using both v1 and v1beta2 API versions)

Steps to reproduce

1. Create a bigquery table with a field with mixed case, such as fooBar
2. Attempt to use JsonStreamWriter to save a record to this table

Stack trace

com.google.api.pathtemplate.ValidationException: Field at index 3 has mismatch names (publishedAt) (publishedat)
    at com.google.cloud.bigquery.storage.v1beta2.JsonToProtoMessage.convertJsonToProtoMessageImpl(JsonToProtoMessage.java:133)
    at com.google.cloud.bigquery.storage.v1beta2.JsonToProtoMessage.convertJsonToProtoMessage(JsonToProtoMessage.java:86)
    at com.google.cloud.bigquery.storage.v1beta2.JsonStreamWriter.append(JsonStreamWriter.java:110)
    at com.google.cloud.bigquery.storage.v1beta2.JsonStreamWriter.append(JsonStreamWriter.java:90)

Any additional information below

This is because the comparison here does not take into account the fact that the protobuf schema always has lower case field names, while the the BQ table schema field may have mixed-cased field names:

java-bigquerystorage/google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/JsonToProtoMessage.java

Line 127 in 9d272dd

if (!fieldSchema.getName().equals(field.getName())) {