WASIX: Align Threads Implementation With Proposed Standard

[theduke]

Align the WASIX threads implementation with the proposed standard: https://github.com/WebAssembly/wasi-threads .

The only relatively minor required change is exposing stack information via globals instead of passing them in the spawn syscall.

[ptitSeb]

Needs some check

[syrusakbary]

This was fixed by #3774 . Closing

[theduke]

No this was not done, we only added support for upstream, we didn't switch WASIX to use the same abi.

[theduke]

@john-sharratt was there a reason for keeping the divergence (pointer arg vs return value)?

[john-sharratt]

WASIX is not going to use the exact same ABI for this while its still under development, once its properly standardized it can be reopened.
WASI threads is already fully supported via its experimental ABI (that's in its own namespace) which is converged into the same implementation and should be fully functional; although we need the community to build some WASI test cases for this to add to the regression suite