This fixes a bug that caused the editor to be rendered incorrectly when
its bounds extended outside the content mask. This is because the editor
uses the returned `Hitbox` bounds to determine the origin of its
elements.
With this commit, we will now store a new `content_mask` field within
the `Hitbox` struct which is captured when the hitbox is inserted. Then,
the content mask is applied on the fly when performing a hit test to
determine whether the hitbox is actually hovered.
Release Notes:
- N/A
Antonio Scandurra
200e36311c