This is a modifier if it appears before an introducer and a control flow
keyword if it appears before `=>`. Use introducer highlighting if it's
neither.
VSCode's JSON parser no longer accepts comments in at least textmate
grammars, so remove the comments. It's unclear whether VSCode changed
here or whether this hasn't worked since the comments were added.
Clean up the textmate grammar: refactor, add some missing operators and
keywords, classify keywords as introducer / modifier as appropriate, fix
comment grammar to require space after `//`, and generalize recognition
of iN, fN, uN to recognize all such type literals.
Be more cautious in language server -- I was seeing frequent crashes for
`IdentifierName` parse nodes whose token was not actually an identifier,
presumably due to error recovery.
Richard Smith
