Add documentation for synchronous access to asynchronous operations

[Copilot]

This PR addresses the common scenario where developers need to call asynchronous methods but cannot use await throughout their call stack. This situation often occurs in legacy codebases or when integrating async methods into synchronous APIs.

The new section "Synchronous access to asynchronous operations" provides practical guidance on:

• GetAwaiter().GetResult() - The preferred approach when blocking is unavoidable, as it preserves original exceptions without wrapping them in AggregateException
• Task.Run wrapper pattern - For complex scenarios where isolating async work on a thread pool thread can help avoid deadlocks
• Wait() and Result - Documented as discouraged approaches due to poor exception handling and higher deadlock risk

The documentation includes:

• Clear warnings about deadlock risks and performance impacts
• Code examples for each approach
• Links to Stephen Toub's authoritative blog post on sync wrappers
• Appropriate emphasis that async/await throughout the call stack remains the preferred solution

This enhancement follows the guidance from @stephentoub and @BillWagner to provide practical options while keeping "dangerous" patterns appropriately cautioned with clear warnings about their risks.

Fixes #37040.

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Internal previews

📄 File	🔗 Preview link
docs/csharp/asynchronous-programming/async-scenarios.md	docs/csharp/asynchronous-programming/async-scenarios

[BillWagner]

This is a good start, I have a few comments.

[BillWagner]

@copilot address the review comments.

[BillWagner]

This is ready for final review.

[learn-build-service-prod]

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[learn-build-service-prod]

PoliCheck Scan Report

The following reports lists PoliCheck issues in PR files. Before you merge the PR, you must fix all severity-1 issues. Other issues are also a high priority. The AI Review Details column lists suggestions for either removing or replacing the terms. If you find a false positive result, mention it in a comment that you post to the PR. The feedback helps reduce false positive instances in future scans.

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[learn-build-service-prod]

PoliCheck Scan Report

The following reports lists PoliCheck issues in PR files. Before you merge the PR, you must fix all severity-1 issues. Other issues are also a high priority. The AI Review Details column lists suggestions for either removing or replacing the terms. If you find a false positive result, mention it in a comment that you post to the PR. The feedback helps reduce false positive instances in future scans.

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