Update to Web IDL changes to optional dictionary defaulting

[inexorabletash]

See: https://github.com/heycam/webidl/issues/758

Web IDL recently changed to require explicitly listing a default value for defaulted dictionaries instead of it just magically happening.

In practice what that means is that APIs like this:

Constructor (BaseAudioContext context, optional AnalyserOptions options)

need to be written like this instead:

Constructor (BaseAudioContext context, optional AnalyserOptions options = {})

(with the addition of = {} on the dictionary argument).

For entries-api:

• FileSystemDirectoryEntry: getFile() and getDirectory()

[inexorabletash]

This should be unblocked now (wpt and bikeshed updated).