Make LanguageRuntime::GetDynamicTypeAndAddress return a ValueType

For C++ and ObjC, dynamic values are always (at least somewhat) pointer-like in nature, so a ValueType of scalar is actually good enough that it could originally be hardcoded as the right choice
Other languages, might have broader notions of things that are dynamic (e.g. a language where a value type can be dynamic). In those cases, it might actually be the case that a dynamic value is a pointer-to the data, or even a host address if dynamic expression results entirely in host space are being talked about

This patch enables the language runtime to make that decision, and makes ValueObjectDynamicValue comply with it

llvm-svn: 247957