Fix spelling errors in documentation

[sbc100]

No description provided.

[hoodmane]

Have you thought about using codespell?
https://github.com/codespell-project/codespell

[sbc100]

This PR is mostly an experiment to see how good Jules is at making PRs (I certainly don't expect to land those spell check scripts that it wrote)

Codespell does look good though.. we should use that !

[tvoeroes]

Hi, you might as well throw this in: In site/source/docs/api_reference/emscripten.h.rst:402 it says emscripten_async_calls instead of emscripten_async_call.

[sbc100]

Hi, you might as well throw this in: In site/source/docs/api_reference/emscripten.h.rst:402 it says emscripten_async_calls instead of emscripten_async_call.

Thanks: #24750