Inspector: Fix PROPERTY_HINT_SPRITE_FRAME not behaving as RANGE

This was a regression in 3.1 and later from the new inspector, where
PROPERTY_HINT_SPRITE_FRAME was not fully re-implemented. It's meant to
be a normal PROPERTY_HINT_RANGE which also automatically increments its
value when keyed in the animation player.

To avoid code duplication, I made the frames properties use the actual
PROPERTY_HINT_RANGE and introduced a PROPERTY_USAGE_KEYING_INCREMENTS
usage flag instead.

editor/editor_inspector.cpp

@@ -504,7 +504,7 @@ bool EditorProperty::use_keying_next() const {
 		PropertyInfo &p = I->get();
 
 		if (p.name == property) {
-			return p.hint == PROPERTY_HINT_SPRITE_FRAME;
+			return (p.usage & PROPERTY_USAGE_KEYING_INCREMENTS);
 		}
 	}