Don't export most things, for mixins

[domenic]

See also #53. is/isImpl and maybe mixedInto make sense. But most of the rest of the exports don't.

To reliably identify a mixin, we can either wait for whatwg/webidl#363 or we can use a custom extended attribute in the meantime.

[TimothyGu]

Are there examples of interfaces defined with NoInterfaceObject but is not a mixin?

[domenic]

A few legacy ones. E.g. https://html.spec.whatwg.org/#external

[TimothyGu]

In that case, could we specifically flag the few NoInterfaceObject non-mixin interfaces and default to the mixin behavior for NoInterfaceObject? I could see the argument against this of course but just thought it might cause less churn.

[domenic]

I think I'd rather tag the mixins since we're going to eventually make mixins first class in Web IDL anyway so it'd be nice to get a sense of which ones they are.

[TimothyGu]

Sounds just fine to me.

[ExE-Boss]

Is this supposed to be closed?

Because README.md says that this is still an issue:

webidl2js/README.md

Line 130 in 9f103a2

Note that all of the below are still exported for "mixin" interfaces, but only `isImpl()` and `is()` make sense ([#55](https://github.com/jsdom/webidl2js/issues/55)).

Also, #68’s description says that it doesn’t fix this.

[TimothyGu]

Ugh, GitHub's auto-closed this issue even though I said:

Note, this does not yet fix #55

Thanks for the note @ExE-Boss!

[ExE-Boss]

Yeah, that’s because you wrote “fix” followed by the issue number separated by a single space (U+0020), which is all GitHub cares about.

[TimothyGu]

Fixed in #135. Interface mixins don’t cause files to be generated.