Without the "mixin" keyword, wasm_bindgen_webidl would report:
Partial interface WindowOrWorkerGlobalScope missing non-partial interface
Also, including the "mixin" keyword here is consistent with the official
webidl spec (for example see https://fetch.spec.whatwg.org/#fetch-method)
I think these might all be from before WebIDL mixins existed. Either way,
multiple inheritance of interfaces that don't have exposed interface objects is
equivalent to mixins.
* Try to enable all webidls
* Separate out unavailable webidl files by reason.
* Create record of fully tested WebIDL files
* Update notes to reflect new situation with web-idl
* Make a blank ident fail, disable the necessary widls.
It turns out that all the blank idents came from blank enum variants,
which is allowed in webidl apparently.
