[lldb] Consult Language plugin in GetDisplayDemangledName (#90294)

Give language plugins the opportunity to provide a language specific
display name.

This will be used in a follow up commit. The purpose of this change is
to ultimately display breakpoint locations with a more human friendly
demangling of Swift symbols.

lldb/include/lldb/Target/Language.h

@@ -281,6 +281,10 @@ class Language : public PluginInterface {
     return mangled.GetMangledName();
   }
 
+  virtual ConstString GetDisplayDemangledName(Mangled mangled) const {
+    return mangled.GetDemangledName();
+  }
+
   virtual void GetExceptionResolverDescription(bool catch_on, bool throw_on,
                                                Stream &s);
 

lldb/source/Core/Mangled.cpp

@@ -310,6 +310,8 @@ ConstString Mangled::GetDemangledName() const {
 }
 
 ConstString Mangled::GetDisplayDemangledName() const {
+  if (Language *lang = Language::FindPlugin(GuessLanguage()))
+    return lang->GetDisplayDemangledName(*this);
   return GetDemangledName();
 }