This is a major change to how webidl is processed. This adds
a two phase process, where the first phase records the names of
various types and indexes the mixins (and might do more in the
future). The actual program building happens in the second phase.
As part of this, this also makes it so that interface objects
are passed by reference, rather than by value. The spec isn't
exactly clear on this, but Mozilla's C++ reflection suggestions
seem to indicate that they should be passed by reference (see
https://developer.mozilla.org/en-US/docs/Mozilla/WebIDL_bindings).
This sets the `catch` flag on the emitted AST when an operation/attribute has
the `[Throws]` extended attribute on it.
Additionally, constructors aren't annotated with `[Throws]` but can still throw
exceptions, so we must conservatively assume *every* constructor can throw an
error.
* webidl: Remove exact-output tests
These have not been as effective, nor as easy to write and maintain, as the
project()-based integration tests.
* tests: Move webidl tests into the webidl crate's test suite
This is still a work in progress. Parse WebIDL source text and convert it into
wasm-bindgen AST, so that we can automatically emit bindings for the types and
functions described in the WebIDL.
