moreuuids: Add GUID defines for common subtitle renderers

Adds VSFilter (auto-loading version) and XySubFilter's GUIDs as
defines into moreuuids.h.
AppSettings: Utilize the VSFilter define

Magic strings begone!
FGManager: Block VSFilter when XySubFilter will get used.

This is generally a temporary solution.

In the future the amount of things in the check might have to
be adapted depending on the implementation of MadVR's subtitle
interface.