Holding shift while scrolling doesn't scroll horizontally #1662
Description
Expected Behavior
Holding shift while using the scroll wheel should scroll left or right based on deltaY.
Actual Behavior
Holding shift while scrolling doesn't change anything.
(Other browsers set deltaX instead of deltaY while shift is held, but Firefox doesn't.)
Steps to Reproduce
Hold shift and use the scroll wheel while running Firefox. Notice that the block workspace scrolls up/down instead of left/right.
Operating System and Browser
Firefox 62.0b10, Debian (testing).
Sort of branching off of #1427 here. This is exactly the same issue as scratchfoundation/scratch-paint#156, which I fixed with in scratchfoundation/scratch-paint#263. Shouldn't be too big of a deal to port the same code to scratch-blocks.