swift234

Provide 'Simplified' demangling mode

To support UI applications displaying demangled names in a limited
amount of screen space, provide a new SwiftDemangle API and Demangler
option to do the following:

- Skip all module name prefixes when printing contexts
- Don't print implicit self/metatype parameters when printing
function types

Add a '-simplified' flag to swift-demangle to support testing at the
command line.

Swift SVN r28727