Move C++ mangle to frontend in windows

This PR introduces windows C++ mangling in frontend.

The main reasons for this work:
1. Current (backend) mangling doesn't always properly process symbols in x86_64 mode. (e.g. function pointers)
2. Current mangling implementation doesn't allow get correct `.mangleof` value (It returns symbol name instead of mangle).
3. Current mangling doesn't process templates.