[lldb][TypeSystemClang] Honor DW_AT_rvalue_reference when creating C++ FunctionPrototypes

Currently funciton lookup in the expression evaluator
fails to disambiguate member functions the are overloaded
on lvalue/rvalue reference-qualifiers. This happens because
we unconditionally set a `FunctionPrototype`s
`ExtProtoInfo::RefQualifier` to `RQ_None`. We lose
the ref-qualifiers in the synthesized AST and `clang::Sema`
fails to pick a correct overload candidate.

DWARF emits information about a function's ref-qualifiers
in the form of a boolean `DW_AT_rvalue_reference` (for rvalues)
and `DW_AT_reference` (for lvalues).

This patch sets the `FunctionPrototype::ExtProtoInfo::RefQualifier`
based on the DWARF attributes above.

**Testing**

* Added API test

llvm/llvm-project issue #57866

Differential Revision: https://reviews.llvm.org/D134661