Transformation cage (#502)

* Render corners and edges of selection box

* Refactor

* Add drag detection

* Implement the transform handles

* Implement rotation by dragging <40px from bounds

* Refine clustered handle behaviour

* Add cursors

* Add snap angle

* Fix MMB drag whilst in select tool

* Convert calculate_pivot into a seperate function

* rename start_vec to start_offset

* Fix typo

* Remove Undo transaction on <10px mouse move

Co-authored-by: Keavon Chambers <keavon@keavon.com>

editor/src/frontend/utility_types.rs

@@ -15,4 +15,14 @@ pub enum MouseCursorIcon {
 	Grabbing,
 	Crosshair,
 	Text,
+	NSResize,
+	EWResize,
+	NESWResize,
+	NWSEResize,
+}
+
+impl Default for MouseCursorIcon {
+	fn default() -> Self {
+		Self::Default
+	}
 }