available() and install() return both promises and throw exceptions

[jan-ivar]

The promise guide says: "promise-returning functions should never synchronously throw errors, since that would force duplicate error-handling logic on the consumer"

Both available() ("throw it and abort these steps") and install() ("throw an InvalidStateError and abort these steps.") appear to violate this.

This must be fixed — the behavior isn't even possible in implementations like Gecko which auto-reject the promise instead of throwing in the WebIDL binding code.

[jan-ivar]

It looks like WPT is already testing the right thing so this is hopefully just editorial (though MDN needs to be updated).

[jan-ivar]

Note technically the prose is fine, as WebIDL does convert these exceptions to rejected promises.

But I'm seeing no precedent for writing it this way, and it did seem to confuse MDN. So we should probably rewrite it to match how WebAudio does it elsewhere.

[padenot]

Indeed, both work, but I've aligned, it was trivial.