Add JoinableTaskFactory.DisableProcessing()

[AArnott]

Sample use case:

jtf.Run(
    async delegate
    {
        jtf.DisableProcessing();
        // Code that cannot afford to be interrupted by COM RPC calls during synchronously blocking calls.
    });

This also enhances the JoinableTaskFactory.WithPriority(Dispatcher) extension method so that it automatically honors calls to Dispatcher.DisableProcessing() to match its behavior.

[Copilot]

Pull request overview

Adds a JoinableTaskFactory.DisableProcessing() API to suppress message pumping (e.g., COM RPC reentrancy via CoWait) during synchronous waits within the ambient JoinableTask, plus tests and samples demonstrating the behavior.

Changes:

• Introduce JoinableTaskFactory.DisableProcessing() and plumb a DisableProcessing flag through JoinableTask and its synchronization context’s Wait override.
• Add .NET Framework STA tests and a COM-based probe (CoWaitMainThreadTransition) to validate CoWait penetration vs. blocking behavior.
• Update samples/docs wiring (new DisableProcessing sample, SuppressRelevance sample ref update) and bump version.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
version.json	Bumps package version to 18.7.
test/Microsoft.VisualStudio.Threading.Tests/NonConcurrentSynchronizationContextTests.cs	Adjusts tuple nullability in an existing test.
test/Microsoft.VisualStudio.Threading.Tests/NoMessagePumpSyncContextTests.cs	Adds STA tests validating no-message-pump waits (NETFRAMEWORK only).
test/Microsoft.VisualStudio.Threading.Tests/JoinableTaskFactoryTests.cs	Adds tests for DisableProcessing() behavior and nesting.
test/Microsoft.VisualStudio.Threading.Tests/CoWaitMainThreadTransition.cs	Adds a COM-based probe to detect whether CoWait/message pumping occurs (NETFRAMEWORK only).
test/Microsoft.VisualStudio.Threading.Tests/AsyncCrossProcessMutexTests.cs	Tweaks abandoned-mutex assertions in TryEnterAsync_AbandonedMutex.
src/Microsoft.VisualStudio.Threading/Strings.resx	Adds NoAmbientTask resource string for the new API exception.
src/Microsoft.VisualStudio.Threading/ReentrantSemaphore.cs	Updates sample code reference for SuppressRelevance.
src/Microsoft.VisualStudio.Threading/NoMessagePumpSyncContext.cs	Refines OS/runtime conditional compilation for Windows detection.
src/Microsoft.VisualStudio.Threading/JoinableTaskFactory.cs	Adds DisableProcessing() public API and ProcessingDisabledOperation token.
src/Microsoft.VisualStudio.Threading/JoinableTask.cs	Adds internal DisableProcessing flag and sync context propagation.
src/Microsoft.VisualStudio.Threading/JoinableTask+JoinableTaskSynchronizationContext.cs	Adds DisableProcessing support and overrides Wait to use WaitForMultipleObjects when enabled.
samples/SuppressRelevance.cs	Renames sample type and fixes a spelling error in a comment.
samples/Polyfill.cs	Adds NETFRAMEWORK polyfill stub used by samples.
samples/DisableProcessing.cs	Adds new sample referenced by the new API docs.
.github/copilot-instructions.md	Clarifies namespace expectations for new files vs. test files.

[Copilot]

Pull request overview

Copilot reviewed 20 out of 20 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated 2 comments.