Update CoreclrTestWrapperLib to use diagnostics IPC for hang dump collection

[tommcdon]

Request dumps for timed-out tests through diagnostics IPC while preserving verbose dump output and detailed failures.

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[Copilot]

🟡 Changes recommended

The new timeout path introduces unbounded waits/long IPC timeouts that can hang or significantly extend CI after a test timeout, and should be made best-effort and bounded.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR updates the CoreCLR test wrapper’s timeout-time crash dump collection on non-Windows platforms to request dumps via the .NET diagnostics IPC socket instead of invoking createdump, and restructures timeout reporting so diagnostic output can be captured and appended to the test output.

Changes:

• Add diagnostics IPC message construction + Unix domain socket client to request GenerateCoreDump3 dumps on non-Windows.
• Route dump-collection logs into an in-memory writer during timeout handling and append them to the test output after killing the timed-out process tree.
• Generalize dump collection helpers to accept TextWriter instead of StreamWriter.

File summaries

File	Description
src/tests/Common/CoreCLRTestLibrary/CoreclrTestWrapperLib.cs	Replace non-Windows dump collection with diagnostics IPC requests and adjust timeout handling/output to capture dump diagnostics.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 2
• Review effort level: Lite

[Copilot]

🟡 Changes recommended

The new diagnostics IPC socket probing and multi-socket handling have correctness issues that can cause dump collection to fail unnecessarily in some environments.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

src/tests/Common/CoreCLRTestLibrary/CoreclrTestWrapperLib.cs:318

• If TMPDIR is set but points to a missing/inaccessible directory, dump collection fails immediately even though the runtime’s diagnostic socket is typically under /tmp. Also, the failure message doesn’t identify which directory/pattern was searched, which makes diagnosing CI/environment issues harder.

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Lite