Saves having this defined in 20+ places. If we ever make any changes to
shear, it's 100% going to need to be applied to every usage (there will
never be a case of multiple different shears in the game).
Also fixes a mismatching definition in `ShearedNub`.
Also includes a test case in `TestSceneShearedButton`s to ensure the buttons' shear factors don't change on different heights (I've encountered issues with that previously).