Revert "Remove obsolete mw-highlighter styles"

The 'direction' rules must not be applied to regular preformatted
text in MediaWiki core, only to syntax-highlighted programming
language code.

(Not reverting the part that removes 'monospace' rule, *that* is
superfluous.)

This reverts commit f834b719b99c5b950d50c27cec86712c30159d25.

Bug: T103780
Change-Id: Ie7e9123ab3456aa6fff0485431fe81cd5eb31fa2