DOMError -> DOMException

Per previous discussions [1][2] highlighted in spec issues, we'd like to
remove DOMError from the platform in favor of using DOMException.

Sanity check: web-compat allowing, should we just swap DOMException in any
place DOMError is currently used?

I've done this (among other unvetted things) in the Indexed DB "v2" ED
[3][4], which exposes `error` attributes, which would now be DOMExceptions.
A Blink CL [5] passes our tests which only inspected name/message
properties. No idea yet if this is web compatible, but it seems likely
other than some test code.

Any IDL concerns about DOMException attributes? Are there expectations that
specs would have e.g. subclasses or typedefs of DOMException? I assume no
and no, but maybe others had a different vision?


[1] https://www.w3.org/Bugs/Public/show_bug.cgi?id=23367
[2] https://www.w3.org/Bugs/Public/show_bug.cgi?id=21740
[3] https://github.com/w3c/IndexedDB/issues/16
[4]
https://github.com/w3c/IndexedDB/commit/42fb5845b9974b95bb0c2c446f893863ec83da2f
[5] https://codereview.chromium.org/1182233003/