[don’t merge] Fix MDFCs being able to be turned face down

[PurpleCrowbar]

Previously, MDFCs could (wrongly) be turned face-down via effects of cards like [[Ixidron]]. This would not apply to TDFCs which had a check in place to prevent this. This PR adds an equivalent check for MDFCs.

[PurpleCrowbar]

[[Ixidron]]

[github-actions[bot]]

Ixidron - (Gatherer) (Scryfall) (EDHREC)

{3}{U}{U} Creature — Illusion / As Ixidron enters the battlefield, turn all other nontoken creatures face down. (They're 2/2 creatures.) Ixidron's power and toughness are each equal to the number of face-down creatures on the battlefield.