llvm-mc/AsmMatcher: Improve match code.

 - This doesn't actually improve the algorithm (its still linear), but the
   generated (match) code is now fairly compact and table driven. Still need a
   generic string matcher.

 - The table still needs to be compressed, this is quite simple to do and should
   shrink it to under 16k.

 - This also simplifies and restructures the code to make the match classes more
   explicit, in anticipation of resolving ambiguities.

llvm-svn: 78461