Can/should we make emscripten_futex_wait/wake API work in Wasm Workers.

[sbc100]

Its doesn't seem like it should be hard to make them work.

It would help us fix things like #26283, and avoid issues like #26309 where folks might think the API was actually working.

Since #21618 it has been possible to call the API when both Wasm Workers and pthreads were enabled, but not when only Wasm Workers is used.

[sbc100]

I think as part of this we should also be able to make emscripten_is_main_runtime_thread work.

[sbc100]

CC @cwoffenden @juj