base javascript: Tweak variable highlighting
base javascript: Tweak variable highlighting

This commit avoids false positives when highlighting literals such as
`$window`, which is a regular variable but still highlighted as a
special value.

Special highlighting of variables that start with a dollar sign `$`
was also removed, as not all variables start with a dollar sign,
and we don't have a reliable way yet to detect variables.

jkonecny12/kakoune,alexherbo2/kakoune,casimir/kakoune,jjthrash/kakoune,occivink/kakoune,danr/kakoune,danr/kakoune,danr/kakoune,mawww/kakoune,lenormf/kakoune,jjthrash/kakoune,occivink/kakoune,alexherbo2/kakoune,lenormf/kakoune,lenormf/kakoune,mawww/kakoune,alexherbo2/kakoune,occivink/kakoune,casimir/kakoune,Somasis/kakoune,Somasis/kakoune,mawww/kakoune,jkonecny12/kakoune,jjthrash/kakoune,casimir/kakoune,danr/kakoune,jkonecny12/kakoune,alexherbo2/kakoune,jjthrash/kakoune,mawww/kakoune,Somasis/kakoune,lenormf/kakoune,occivink/kakoune,Somasis/kakoune,jkonecny12/kakoune,casimir/kakoune