Only scroll one axis at a time, whichever has the greater delta

[nathansobo]

Fixes #15239

This PR fixes a logic error in the following line of code:

const scrollPositionChanged =
  this.setScrollLeft(this.getScrollLeft() + deltaX) ||
  this.setScrollTop(this.getScrollTop() + deltaY)

I didn't account for the "short-circuit" behavior of the or statement. With this code, we first attempt to scroll horizontally by deltaX, and if we scroll even a little, then we never attempt to scroll vertically. When I tested this originally, I thought we were getting the "one axis at a time" behavior automatically somehow, but really I was just seeing this bug. 🙈

This PR restores the behavior prior to 1.19 of scrolling only on one axis at a time, whichever has the greater delta.

[nathansobo]

/cc @as-cii