[lldb][DebugNamesDWARF] Also use mangled name when matching regex

When LLDB queries the debug names index with a regex, we should use the
`Mangled` class wrapper, which attempts to match regex first against the mangled
name and then against the demangled name. It is important to do so, otherwise
queries like `frame var --regex A::` would never work. This is what is done for
the Apple index as well.

This fixes test/API/lang/cpp/class_static/main.cpp when compiled with DWARF 5.

Differential Revision: https://reviews.llvm.org/D154617

lldb/source/Plugins/SymbolFile/DWARF/DebugNamesDWARFIndex.cpp

@@ -104,7 +104,8 @@ void DebugNamesDWARFIndex::GetGlobalVariables(
     llvm::function_ref<bool(DWARFDIE die)> callback) {
   for (const DebugNames::NameIndex &ni: *m_debug_names_up) {
     for (DebugNames::NameTableEntry nte: ni) {
-      if (!regex.Execute(nte.getString()))
+      Mangled mangled_name(nte.getString());
+      if (!mangled_name.NameMatches(regex))
         continue;
 
       uint64_t entry_offset = nte.getEntryOffset();