[codeview] Improve names of types in scopes and member function ids

We now include namespace scope info in LF_FUNC_ID records and we emit
LF_MFUNC_ID records for member functions as we should.

Class names are now fully qualified, which is what MSVC does.

Add a little bit of scaffolding to handle ThisAdjustment when it arrives
in DISubprogram.

llvm-svn: 273358