Use the "font encoding" property as a base direction hint

Use the "font encoding" property as a base direction hint

ASS specifies a "font encoding", both in the styles as well as with
the \fe override tag. This font encoding is very Windows-specific
and libass doesn't use it for charmap matching or anything like
that. However, it can be useful for hinting the base direction of
text. Make Hebrew and Arabic encodings switch to RTL base direction,
other languages to LTR and use neutral base direction for the
autodetect setting.