Use ParserOptions language instead of RequestContext language

The context user language is correctly set to that of the user
who is saving the page.

Parser options are set to the default language during saving and
only changed to the user language when viewing the page with
a uselang that is not the default wiki language.

As a result we were saving the user language (e.g. French) on
en.wikipedia.org as the canonical version on-save and only changing
it to the correct language for non-English viewers.

To test:
* Wiki set to 'en', user preference language to 'nl'
* Save a page with templatedata
* View it logged-out without a uselang query

Was 'nl', is now 'en'.

Bug: 52419
Change-Id: Ic8b5b63450c9f80b85a95d16cc81ce62fc96b77f
Merge "Use ParserOptions language instead of RequestContext language"