LibCMake: Add folding regions to syntax highlighter

This creates folding regions for blocks defined by the following:
- if/elseif/else/endif
- foreach/endforeach
- while/endwhile
- macro/endmacro
- function/endfunction

Since there is no guarantee that each keyword will have a matching
partner, we do our best by looking for the most recent possible start
token matching the current end token. If we find one, we link to it and
drop all the other start-tokens that happened in between. For example,
we would define a folding region for this invalid file like so:

[-] if(TRUE)
 │      while()
 └─ endif()

0 files changed, 0 insertions, 0 deletions