A large portion of the modules implementation in SpiderMonkey is written in self-hosted JS (js/src/builtin/Module.js). There were good reasons to do this at the time, but this hasn't really been a win overall.

Moving this code to C++ would improve:

• security: prototype pollution attacks would not be possible
• efficiency: currently execution bounces repeatedly between JS and native code which is not optimal, and all data must uses JS types even when native types would be preferable=
• debugging: currently there's no debugger support for backtraces through JS stack frames making it harder to investigate issues in the module implementation

Reimplement ModuleGetExportedNames in C++ and remove from self-hosted code.
This adds an intrinsic for it so that the remaining self-hosted code can call
it. This will be removed eventually.

Depends on D149880

Depends on D149881

Depends on D149882

Depends on D149883

Depends on D149884

This also renames it GatherAvailableModuleAncestors which is what it's called
in the spec now.

Depends on D149885

https://hg.mozilla.org/mozilla-central/rev/95b47c5e977c
https://hg.mozilla.org/mozilla-central/rev/90b8eff04bf8
https://hg.mozilla.org/mozilla-central/rev/8e18e606b42c
https://hg.mozilla.org/mozilla-central/rev/78781f9739fa
https://hg.mozilla.org/mozilla-central/rev/b609fcb74109
https://hg.mozilla.org/mozilla-central/rev/353db52eac26
https://hg.mozilla.org/mozilla-central/rev/0cacfd0aec5d