swift234

Add CharSourceRange -- a half-open character range, which will be used in IDE
integration

Motivation: libIDE clients should be simple, and they should not have to
translate token-based SourceRanges to character locations.

This also allows us to remove the dependency of DiagnosticConsumer on the
Lexer.  Now the DiagnosticEngine translates the diagnostics to CharSourceRanges
and passes character-based ranges to the DiagnosticConsumer.


Swift SVN r7173