swift234

SourceKit: Clean up syntax map switch

When creating the token map for highlighting, there is some glitchy
behavior that needed to be cleaned up:

- New image literal syntax wasn't getting highlighted as an object
  literal keyword.
- Other #-prefixed keywords had no data
- #line would appear as a build config ("brown") at the start of a line
- #available showed up as a build config. However, this should be a keyword
  because it is a runtime check, not a build configuration.

Add some test cases for these.

Fixes:
rdar://problem/26451674