WIP: Support WebIDL modules

[ghost]

Fixes #1740 (eventually); adds support for WebIDL modules.

Related: rustwasm/weedle#31

[alexcrichton]

Looking reasonable to me! Could you expand a bit on the expected impact of web-sys as well?

[ghost]

@alexcrichton thanks! I will open a companion PR for weedle in a bit.

Regarding the expected impact on web-sys, I haven't thought too much about that yet. The goal is that code generation for webidls that don't use modules should remain unchanged. There should be opportunities to benefit from supporting modules going forward though.

The main motivation for this right now is to bring more flexibility for writing webidls for things like electron and node and other larger libraries that are difficult to fully cover with wasm-bindgen-cli and not currently possible to model accurately with wasm-bindgen-webidl.

If y'all have thoughts about how this might impact web-sys or other parts of the ecosystem, I'd be interested to here more about that.

[alexcrichton]

Ok cool sounds good, I mostly just wanted to double check that this doesn't change much of the current APIs. For generating new ones it might be neat to generate a literal Rust module for a WebIDL module perhaps? That coupled with the unstable attributes I think should be sufficient here

[ghost]

I'm going to close this since I've put the parser rewrite on hold to focus on other things I'm not sure if/when I'll be able to get back to it. I still think it would be a good idea to support webidl module syntax at some point. Thanks for the feedback!