Replace SHash of call counting managers with linked list.

[rcj1]

We only add, remove, and iterate through all here - we never make use of the hashing behavior. So, it is more appropriate to have this as a linked list as opposed to an SHash.

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[Copilot]

Pull request overview

This PR simplifies call counting manager tracking in CoreCLR by replacing an SHash that was only used for add/remove/iterate with a lightweight linked-list, and adjusts startup initialization accordingly.

Changes:

• Replace the global SHash of CallCountingManager instances with an intrusive linked list (O(1) add/remove, simple iteration).
• Remove CallCountingManager::StaticInitialize() and call CallCountingStub::StaticInitialize() directly during EE startup.
• Update all iterations over managers to traverse the linked list.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/coreclr/vm/ceemain.cpp	Switch tiered compilation startup init from CallCountingManager::StaticInitialize() to CallCountingStub::StaticInitialize().
src/coreclr/vm/callcounting.h	Remove manager SHash traits/storage; add linked-list fields and update static storage type.
src/coreclr/vm/callcounting.cpp	Implement linked-list insertion/removal and update all manager iteration sites; delete unused hash-traits and static init.