swift234

This commit implements the Demangler API in C++ and de facto deprecates the existing Demangle.swift

The new demangler is in the "swift/SIL/Demangle.{h|cpp}" files, and in the swift::Demangle namespace, which has two public entry points:

std::string demangleSymbol(llvm::StringRef mangled);
std::string demangleType(llvm::StringRef mangled);

This was necessary to support the need for LLDB to demangle Swift symbol (and type) names

Test case is included



Swift SVN r6547