Make mouse wheel a Vector2, implement initial horizontal mouse wheel support for UI MouseWheel -> MouseScroll, obsolete old Ignore scroll if it's not moving in the same direction that the panel overflows in e.g. stops us interfering with vertical scrolls on horizontally scrolling panels: https://files.facepunch.com/alexguthrie/1b3011b1/sbox-dev_12znz25nJC.mp4 Invert scroll X axis Update some more places where I forgot to change MouseWheel to MouseScroll, obsolete `Input.MouseWheel` and `InputData.MouseWheel` WorldInput uses Vector2 for scroll Pass keyboard modifiers to mouse wheel event, and interpret mouse scrolls as horizontal if shift key is held Invert scroll value for emulated horizontal scroll (scrolling down should scroll to the right)