Validate that all IDL types are defined somewhere

[foolip]

No description provided.

[tidoust]

@dontcallmedom I note that the WebIDL parser in Reffy has a similar list to avoid flagging well-known types as dependencies:
https://github.com/w3c/reffy/blob/master/src/cli/parse-webidl.js#L352

Comparing the two lists (leaving aside void and types defined by other specs), I note the following differences:

• ArrayBufferView in Reffy's WebIDL parser list but not here
• BufferSource in Reffy's WebIDL parser list but not here
• DOMException in Reffy's WebIDL parser list but not here
• DOMTimeStamp in Reffy's WebIDL parser list but not here
• Error in Reffy's WebIDL parser list but not here
• Function in Reffy's WebIDL parser list but not here
• RegExp in Reffy's WebIDL parser list but not here
• VoidFunction in Reffy's WebIDL parser list but not here
• symbol here but not in Reffy's WebIDL parser list

Most of them are from section 4 in WebIDL and can probably be removed from Reffy's WebIDL parser list because they get defined as "real" WebIDL structures.

I'm not sure why Error and RegExp are in Reffy's WebIDL parser list.

Last one is symbol, which seems correct but does not appear in any spec that defines some WebIDL.

I don't think that any change is needed here. Obviously, "DRY" could be an idea but then lists should not have to change often so probably not worth the hassle.

[tidoust]

I created w3c/reffy#516 to possibly refresh the list in Reffy.