Try harder to avoid parser cache pollution

Try harder to avoid parser cache pollution

* ParserOptions is reorganized so it knows all the options and their
  defaults, and can report whether the non-key options are at their
  defaults.
* Definition of the "canonical" ParserOptions (which is unfortunately
  different from the "default" ParserOptions) is moved from
  ContentHandler to ParserOptions.
* WikiPage uses this to throw an exception if it's asked to cache
  with options that aren't used in the cache key.
* ParserCache gets some temporary code to try to avoid a massive cache
  stampede on upgrade.

Bug: T110269
Change-Id: I7fb9ffca96e6bd04db44d2d5f2509ec96ad9371f
Depends-On: I4070a8f51927121f690469716625db4a1064dea5