[RemoteInspection] Store the payload TypeRef of indirect enum payloads
EnumTypeInfoBuilder will build FieldInfos of indirect enum payloads with
the TypeRef set to Builtin.NativeObject.
EnumTypeInfoBuilder has access to the typeref of the type behind the
pointer, which currently isn't saved anywhere.
RemoteInspection clients like LLDB have to re-query it, and read
metadata to find out what the type behind the reference it.
This patch adds a field to FieldInfo with the payload TypeRef, the
one behind the reference.
rdar://170684760