swift234

Diagnostics: use builder pattern instead of streaming for ranges/fix-its.

Per Chris's feedback and suggestions on the verbose fix-it API, convert
diagnostics over to using the builder pattern instead of Clang's streaming
pattern (<<) for fix-its and ranges. Ranges are included because
otherwise it's syntactically difficult to add a fix-it after a range.

New syntax:

  diagnose(Loc, diag::warn_problem)
    .highlight(E->getRange())
    .fixItRemove(E->getLHS()->getRange())
    .fixItInsert(E->getRHS()->getLoc(), "&")
    .fixItReplace(E->getOp()->getRange(), "++");

These builder functions only exist on InFlightDiagnostic; while you can
still modify a plain Diagnostic, you have to do it with plain accessors
and a raw DiagnosticInfo::FixIt.

Swift SVN r4894