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

include/swift/Basic/SourceManager.h

@@ -107,6 +107,9 @@ public:
   /// \brief Returns the offset in bytes for the given source location.
   unsigned getLocOffsetInBuffer(SourceLoc Loc, unsigned BufferID) const;
 
+  /// \brief Returns the distance in bytes between the given source locations.
+  unsigned getByteDistance(SourceLoc Start, SourceLoc End) const;
+
   std::pair<unsigned, unsigned> getLineAndColumn(SourceLoc Loc,
                                                  int BufferID = -1) const {
     assert(Loc.isValid());