Move wfEscapeWikiText() to Parser::escapeWikitext()

Move wfEscapeWikiText() to Parser::escapeWikitext()

wfEscapeWikiText() used $wgEnableMagicLinks, but that could result in an
inconsistency when something modifies the magic link related
ParserOptions.

In general, most uses of wfEscapeWikiText() are in parser functions or
when message parsing, so the Parser is a logical place for it.

A future patch will make it easy to use Parser::escapeWikitext() in
message parameters.

Change-Id: I0fd4d5c135541971b1384a20328f1302b03d715f