Add tvOS export support

[256ArtsDeveloper]

There is currently no tvOS support, only iOS and macOS.

[Calinou]

Closing, as this is not an issue with the iOS plugins specifically, but a missing feature in the engine.

See godotengine/godot#58977 and godotengine/godot#58976 (and the original proposal godotengine/godot-proposals#224), but these PRs have stalled and need to be salvaged by someone else.