Move rust-mozjs's build script to mozjs-sys

[wusyong]

Move all build scripts into mozjs-sys crate which is more conventional when binding FFI.
This can also make possible future changes like linking binary build instead of building everything from source easier.

I added another commit to rename original mozjs-sys's jsglue.cpp to jsapi.cpp, and kept rust-mozjs's jsglue.
It's just clearer IMHO. Let me know if there are better names.

[sagudev]

On one hand jsglue requires headers from mozjs_sys so it might make sense move it there, but on the other hand jsglue provide high level wrappers, that are tightly coupled with stuff in rust-mozjs so it also makes sense to put it there. Moving also violates idea of raw bindings in sys crate ...

I am pretty diverged about this, but I am slightly more in favor to keep things as they are.

So I would love to hear what others think about this and if they are any other reasons for/against this.

[wusyong]

If it's higher level wrappers, it should be implemented by Rust using sys crate directly.
Having another build script to compile and bindgen C++ code makes the structure a bit more complicated.
I'm okay if this module should stay in rust-mozjs, but I think it's better to rewrite in Rust.

[wusyong]

@sagudev Is it possible to push this PR again? I've rebased the PR to latest main branch.
It will still be the same files but they will be inside the same OUT_DIR at least.
This should make #439 easier.

[sagudev]

The more I think about it the more I like it.

To sum up here is how new structure looks like (currently jsapi contains some higher stuff too):

• jsapi.cpp is low level (includes headers for bindings, contains replacement types).
• jsglue.cpp is place for higher level glue (mozilla::maybe wrappers, all other stuff that is not usable via bindgen directly due to cxx).

[sagudev]

@jdm what do you think about this?

[Redfire75369]

I'm not arguing for either option, but I will note that the current split between mozjs-sys's jsglue.cpp and mozjs's jsglue.cpp has no consistent rhyme or reason, some cleanup would be required there regardless of the outcome.

[jdm]

This seems like a reasonable choice!

[wusyong]

Thanks for merging!