Moved a static field initialization from Thread to ProcessorIdCache

[VSadov]

Fixes: #113949

Presence of .cctor in Thread can cause circular dependency if Lock needs to block while Thread .cctor has not run yet.

1. Lock needs to wait on a WaitHandle
2. WaitHandle needs Thread.CurrentThread
3. if Thread's .cctor has not run yet, it needs to run.
   (it is unusual for this to be the first use of Thread, but the activation pattern in Stack overflow from static constructors taking locks on Native AOT #113949 made it possible)
4. .cctor needs to take a Lock, so we go to #1

[Copilot]

Pull Request Overview

This PR moves the static field initialization for processor speed checking from Thread to ProcessorIdCache to resolve a circular dependency issue during static initialization.

• Moved the speed check static field from Thread.cs to ProcessorIdCache.cs.
• Updated GetCurrentProcessorId methods to use the new initialization logic directly from ProcessorIdCache.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/libraries/System.Private.CoreLib/src/System/Threading/Thread.cs	Removed static field initialization and modified GetCurrentProcessorId to call ProcessorIdCache.
src/libraries/System.Private.CoreLib/src/System/Threading/ProcessorIdCache.cs	Added static field initialization and embedded fast-path logic within GetCurrentProcessorId.

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[jkotas]

I assume that this is backport candidate.

[VSadov]

I assume that this is backport candidate.

I think so. The fix is low-risk and we see actual WER buckets due to this.

[jkotas]

/backport to release/9.0-staging

[github-actions]

Started backporting to release/9.0-staging: https://github.com/dotnet/runtime/actions/runs/14270864630

[VSadov]

Thanks!! I was just waiting for PR to get green as that leaves fewer doubts, but it looks like the failures are not specific to the PR.