[codeview] Make function names more consistent with MSVC

Names in function id records don't include nested name specifiers or
template arguments, but names in the symbol stream include both.

For the symbol stream, instead of having Clang put the fully qualified
name in the subprogram display name, recreate it from the subprogram
scope chain. For the type stream, take the unqualified name and chop of
any template arguments.

This makes it so that CodeView DI metadata is more similar to DWARF DI
metadata.

llvm-svn: 273009