Add gRPC JSON transcoding option for case insensitive field names

[JamesNK]

Description

Add a FieldNamesCaseInsensitive setting to gRPC JSON transcoding.

Fixes #50401

[Copilot]

Pull Request Overview

This PR adds a FieldNamesCaseInsensitive option to the gRPC JSON transcoding feature, allowing case-insensitive matching of field names during JSON deserialization.

Key changes:

• Added a new FieldNamesCaseInsensitive boolean property to GrpcJsonSettings class
• Modified the JSON serializer configuration to respect the case-insensitive setting
• Added comprehensive test coverage for the new functionality

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
GrpcJsonSettings.cs	Added the new FieldNamesCaseInsensitive property with documentation explaining interoperability concerns
JsonConverterHelper.cs	Updated to configure PropertyNameCaseInsensitive based on the new setting
MessageTypeInfoResolver.cs	Removed unused import statement
JsonConverterReadTests.cs	Added extensive test cases to verify case-insensitive field matching behavior
transcoding.proto	Added test message type for field name case testing

Comments suppressed due to low confidence (1)

src/Grpc/JsonTranscoding/test/Microsoft.AspNetCore.Grpc.JsonTranscoding.Tests/ConverterTests/JsonConverterReadTests.cs:515

• This test case for MapKeyBool_CaseInsensitive is missing the settings parameter to enable case-insensitive matching. It should include settings: new GrpcJsonSettings { FieldNamesCaseInsensitive = true } to properly test the case-insensitive functionality.

        AssertReadJson<HelloRequest>(json, serializeOld: false);