Make js config handling more robust when config is not in ParserCache

Also improve/add test case for OutputPageJsConfigHookHandler

Also moves wbExperimental out of parser cache, since
this is something that would be good to change more easily
and should not be much of a performance issue to add
in output page.

Change-Id: Ie956b97bd632a0f6863a311fe0a8aff1a9319ea9
(cherry picked from commit 9acaac26d5e9aff33e708de5a3fca61febeda170)