Add UseSTASynchronizationContext to STATestMethod

[Youssef1313]

Fixes #5729

[Copilot]

Pull request overview

This PR adds a UseSTASynchronizationContext property to STATestMethodAttribute to enable preserving the STA thread context for async continuations. When enabled, the attribute creates a custom SynchronizationContext that ensures async continuations run on the same STA thread, which is useful for testing UI components that require STA threading.

Changes:

• Introduced SingleThreadedSTASynchronizationContext class that manages a dedicated STA thread and routes all operations to it
• Added UseSTASynchronizationContext property to STATestMethodAttribute with default value of false
• Modified STATestMethodAttribute.ExecuteAsync to conditionally use the new synchronization context
• Added tests to verify both default behavior (no sync context) and new behavior (with sync context)

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/TestFramework/TestFramework/Attributes/TestMethod/SingleThreadedSTASynchronizationContext.cs	New internal class that implements a custom SynchronizationContext with a dedicated STA thread for routing operations
src/TestFramework/TestFramework/Attributes/TestMethod/STATestMethodAttribute.cs	Added UseSTASynchronizationContext property and modified ExecuteAsync to optionally use the new sync context
src/TestFramework/TestFramework/PublicAPI/PublicAPI.Unshipped.txt	Added public API entries for the new property getter and setter
test/UnitTests/MSTest.SelfRealExamples.UnitTests/STATestMethodSyncContext.cs	Added integration tests verifying both default and new behavior

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.