Emscripten support: Use es6 modules

[hoodmane]

We are in the future and ES6 module support is finally universal in mainstream JavaScript runtimes (Firefox was the straggler but finally added Module WebWorker support in v114 released on June 6 2023). They have many benefits, such as fewer global variables and more sanity. We should switch to using them.

cc @freakboy3742

Linked PRs

• gh-126898: Emscripten support: Use es6 modules #126903

[sobolevn]

Thank you!