[wasm] proper startup sequence in dotnet.worker.js

[pavelsavara]

• pass configuration from main thread
• run relevant parts of startup sequence
• make worker long lived that that we could schedule mono jobs in worker and use promises

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We compile dotnet.worker.js with -s EXPORT_ES6, so it used import(uri).then(callback) dynamic imports to bring in scripts.

There is still a polyfill for Node in the worker JS file that uses require and eval. It could be compiled out if we change the threaded build to not set node as an environment when we build for threading, see

https://github.com/emscripten-core/emscripten/blob/6577be0d782368893b8d0c2dbaac3908fc425ef6/src/settings.js#L615-L640

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Original issue

• the dotnet.worker.js has require in it, which makes it not ES6 ready
• the dotnet.worker.js has eval in it which makes it CSP issue

We could implement some post-link build step, which would append and prepend code to the emscripten's code in dotnet.worker.js4
Or we could just have our own version, which we would have to keep in sync with upstream.

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Issue Details

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• the dotnet.worker.js has require in it, which makes it not ES6 ready
• the dotnet.worker.js has eval in it which makes it CSP issue

We could implement some post-link build step, which would append and prepend code to the emscripten's code in dotnet.worker.js4
Or we could just have our own version, which we would have to keep in sync with upstream.

Author:	pavelsavara
Assignees:	pavelsavara
Labels:	arch-wasm, area-Build-mono
Milestone:	-

[lambdageek]

Couple of things:

1. If you compile with -s EXPORT_ES6, the worker.js is built differently. it does this

   https://github.com/emscripten-core/emscripten/blob/25591f37aa77c415af9c54bc74d073f4653d22d7/src/worker.js#L154-L160

2. We might still need our own version of worker.js since we may need to customize Module before it's passed to createDotnetRuntime, as we noted here [wasm-mt] Add MessageChannel between browser thread and new pthreads #70908 (comment)

[lambdageek]

worker.js seems to only add require if ENVIRONMENT_MAY_BE_NODE is true, which seems like it is set here
https://github.com/emscripten-core/emscripten/blob/2391bfcacbd0396a1cda21843cf3c6a216e6a142/emcc.py#L294

settings.ENVIRONMENT_MAY_BE_NODE = not settings.ENVIRONMENT or 'node' in environments

so we could omit node from -s ENVIRONMENTS=... when we build with threading

[lambdageek]

Just want to add now that the #70746 ES6 PR is merged that dotnet.worker.js is able to load the ES6 dotnet.js module, the node code at the beginning that uses require is skipped.

So the things left to address are to make sure we initialize Module with all the values that our code receives when we load dotnet.js on the main browser thread.

[pavelsavara]

@lambdageek I moved this to 8, please let me know if you think we need it in net7