The ones that match the normal attribute syntax (e.g. `@inline(never)`)
don't need to be recognized as their own node type. They are now handled
by the highlight queries, using a regex on the attribute name. A new
`annotation.builtin` face is applied to them if the user wants them to
be decorated specially. Other attributes also have a new `annotation`
face instead of using `keyword` (although the base configuration just
inherits `keyword`'s appearance).

The two builtin attributes with special syntax -- `@objc` and
`@Available` -- remain in their own nodes.