The `tex_math_dollars` extension is now supported for `dokuwiki`
(but off by default).
Content inside `<latex>...</latex>` is parsed as raw LaTeX inline,
and inside `<LATEX>..</LATEX>` as raw LaTeX block.
In addition, this commit changes the behavior of `<php>...</php>` so
that instead of producing a code block, it produces raw HTML
with `<?php ... ?>`.
Closes#8178.
