Fix Polygon2D undo on transforming vertices

[aXu-AP]

Fix #83657
Instead of checking the mode we are in, check for exceptions that are handled elsewhere. Add checks if we are transforming polygon with move, rotate or scale tool.

Also removes extraneous comments in this block, as undo-redo action name is self-explanatory.

[aXu-AP]

Updated.
After thinking a bit, my initial idea for just excluding actions isn't future-proof. If some other actions were added (for example, #83612 ), extra checks would've needed to be added.
On the other hand, if somebody adds action which transforms polygon, it would be expected to add undo functionality then (ie. adding cases to the switch statement).

[akien-mga]

Thanks!