Where possible, we should move JavaScript to native/wasm code

[sbc100]

This is meta-issue for ongoing work for move as much code as possible out of JavaScript
and into C/C++.

In particular it would be good to focus of code that does HEAP access from JavaScript.
Doing this instead from native code has several advantages:

• The syntax for heap access in JS much harder to read and write
• JS heap access is currently slow when using ALLOW_MEMORY_GROWTH and USE_PTHREADS
• Supporting wasm32 and wasm64 with the same JS code adds complexity ([wasm64] making JS bindings wasm64 aware #12869)

[sbc100]

See #21379 and #22158