Deprecate OutputPage::parse() and OutputPage::parseInline()

Deprecate OutputPage::parse() and OutputPage::parseInline()

The OutputPage::parse() and OutputPage::parseInline() methods behave
misleadingly different from the OutputPage::addWikitext*() methods:
they don't tidy their output, they have different defaults for
interface/content language selection, and they (sometimes) add
wrapper divs.  Deprecate these and add new methods with tidy output,
clear language selection, and consistent defaults:
OutputPage::parseAsContent(), OutputPage::parseAsInterface(),
and OutputPage::parseInlineAsInterface().

Unify the implementation of the parse* methods with the addWikiText*
methods, to reduce the likelihood that the behavior will diverge again
in the future.

Bug: T198214
Change-Id: Ica79c2acbc542ef37f971c0be2582ae771a23bd0