Move local thread pool work items to global by default when blocking on a task

[kouvel]

• Enables the change in Transfer ThreadPool local queue to high-pri queue on Task blocking #109841 by default
• A worker thread blocking on a task while having pending local work items can lead to priority inversion and deadlock-like issues, as local work items are stolen with the lowest priority by other threads. In a situation where all worker threads are blocked on tasks and new ones continue to block on tasks similarly, the global queues may not deplete for a long time and any local work items of blocked threads may not run meanwhile. There have been some reports of issues like this occurring while coinciding with other external issues that aggravate the problem.
• When a worker thread blocks on a task, the change moves any local work items to the high-priority global queue. Using the normal-priority queues can lead to other priority inversion issues in worst-case scenarios like above, where the normal-priority queues may consist of a number of new requests, and local work items typically represent already in-flight work.

[Copilot]

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

Comments suppressed due to low confidence (1)

src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolWorkQueue.cs:723

• The new behavior of moving local work items to a high-priority global queue when blocking on a task should be covered by tests.

internal static void TransferAllLocalWorkItemsToHighPriorityGlobalQueue()

[stephentoub]

Thanks

[kouvel]

Rebased to try tests in latest