[wasm][coreclr] Add RhpNewFast allocators

[radekdoulik]

No description provided.

[Copilot]

Pull Request Overview

This PR implements three previously stubbed-out fast allocation functions (RhpNewFast, RhpNewFastAlign8, and RhpNewFastMisalign) in the portable CoreCLR runtime. These functions provide optimized object allocation paths by attempting to allocate directly from the thread's allocation context before falling back to slower allocation methods.

Key Changes:

• Replaced PORTABILITY_ASSERT stubs with full implementations for all three allocator functions
• Added thread-local allocation context management with fast-path allocation logic
• Implemented alignment handling for 8-byte aligned and misaligned allocations using dummy objects

[dotnet-policy-service]

Tagging subscribers to this area: @mangod9
See info in area-owners.md if you want to be subscribed.

[jkotas]

I have noticed that a few of the existing helpers in this file have unnecessary return null; after RhExceptionHandling_FailedAllocation. Could you please delete it while you are on it?

[jkotas]

I have noticed that a few of the existing helpers in this file have unnecessary return null; after RhExceptionHandling_FailedAllocation. Could you please delete it while you are on it?

Could you please fix this too?

[radekdoulik]

Hope I didn't forget anything else.

[radekdoulik]

Ah, I did, I wanted to ifdef the align8/misalign