Async troubleshooting and pitfalls

[BillWagner]

Contributes to #17714

1. Create common-async-bugs.md — from "Psychic Debugging of Async Methods." Covers the 4 most common bugs: method runs synchronously despite async, can't await void, deadlocks with SynchronizationContext, Task<Task> unwrapping. Also incorporate mentions of UI deadlocks (from "Await and UI and deadlocks") and static constructor deadlocks as warning notes.
2. Create async-lambda-pitfalls.md — from "Potential pitfalls to avoid when passing around async lambdas." Covers: async lambdas assigned to Action delegates (becomes async void), Parallel.ForEach with async lambdas, Task.Factory.StartNew returning Task<Task>.
3. Decompose relevant Async/Await FAQ content into both articles (FAQ answers about async void, Task.Wait vs await, the async keyword not forcing asynchrony).
4. Add both to TOC. Consider grouping under a new "Best practices and troubleshooting" sub-section.

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Internal previews

📄 File	🔗 Preview link
docs/navigate/advanced-programming/toc.yml	docs/navigate/advanced-programming/toc
docs/standard/asynchronous-programming-patterns/async-lambda-pitfalls.md	Async lambda pitfalls
docs/standard/asynchronous-programming-patterns/common-async-bugs.md	Common async/await bugs

[Copilot]

Pull request overview

Adds two new async/await troubleshooting articles to the .NET async programming patterns documentation, with accompanying C# and Visual Basic snippet projects, and wires the new content into the Advanced .NET programming navigation TOC.

Changes:

• Adds common-async-bugs.md covering common async/await failure modes and fixes.
• Adds async-lambda-pitfalls.md covering common mistakes when passing async lambdas to synchronous delegate APIs.
• Adds runnable C# and VB snippet projects for both articles, and links the new pages in the navigation TOC.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
docs/standard/asynchronous-programming-patterns/common-async-bugs.md	New conceptual article about common async/await bugs and mitigations.
docs/standard/asynchronous-programming-patterns/async-lambda-pitfalls.md	New conceptual article about async lambda pitfalls and correct patterns.
docs/navigate/advanced-programming/toc.yml	Adds a “Best practices and troubleshooting” subgroup with links to the new articles.
docs/standard/asynchronous-programming-patterns/snippets/common-async-bugs/csharp/Program.cs	C# snippet source for common async bug examples/fixes.
docs/standard/asynchronous-programming-patterns/snippets/common-async-bugs/csharp/CommonAsyncBugs.csproj	C# snippet project for building/running the common-async-bugs snippets.
docs/standard/asynchronous-programming-patterns/snippets/common-async-bugs/vb/Program.vb	VB snippet source for common async bug examples/fixes.
docs/standard/asynchronous-programming-patterns/snippets/common-async-bugs/vb/CommonAsyncBugs.vbproj	VB snippet project for building/running the common-async-bugs snippets.
docs/standard/asynchronous-programming-patterns/snippets/async-lambda-pitfalls/csharp/Program.cs	C# snippet source for async lambda pitfall examples/fixes.
docs/standard/asynchronous-programming-patterns/snippets/async-lambda-pitfalls/csharp/AsyncLambdaPitfalls.csproj	C# snippet project for building/running the async-lambda-pitfalls snippets.
docs/standard/asynchronous-programming-patterns/snippets/async-lambda-pitfalls/vb/Program.vb	VB snippet source for async lambda pitfall examples/fixes.
docs/standard/asynchronous-programming-patterns/snippets/async-lambda-pitfalls/vb/AsyncLambdaPitfalls.vbproj	VB snippet project for building/running the async-lambda-pitfalls snippets.