Deprecate additional public methods of Parser

Deprecate additional public methods of Parser

Affected:
Parser::armorLinks()
Parser::makeKnownLinkHolder()
Parser::getImageParams()
Parser::parseLinkParameter()
Parser::stripAltText()

It wasn't obvious there was a better name for these, so just rename
them with a `...Private` suffix and deprecate the old names.  When
the deprecated public methods are removed we'll rename the private
methods to remove the `...Private` suffix again.

Code search:
https://codesearch.wmflabs.org/deployed/?q=armorLinks%7CmakeKnownLinkHolder%7CgetImageParams%7CparseLinkParameter%7CstripAltText&i=nope&files=&repos=

Bug: T236810
Change-Id: I44458490fa86abd0ead048a4c94021da6be333f0
(cherry picked from commit 736b6b27f3dc1e9f7b4facc55f08dbc28da68827)