Further polishing of G/R/S visualization and features

[mTvare6]

Followup to #2229.
Fixes https://discord.com/channels/731730685944922173/881073965047636018/939265895509925898.

• In G, we can type a number and it applies to the X axis. That shouldn't happen unless an axis was first chosen.
• We need the 0-9 hint showing at any time you can begin typing a number (so that's always except in unconstrained G). Likewise for a - hint to show you can negate the value.
• A one-frame visual bug: if you S, Y, move the mouse so the scale becomes negative, then Y to turn it to a local scale; for one frame it becomes un-inverted:
• In R mode, there should be no separator line at the very end of the hints bar, when nothing comes after it.
• All G/R/S modes and states need to have a separate section at the start for left click or Enter to confirm and right click or Esc to cancel (copy latter from the hints when drawing a line, and adapt it for the former case).
• Removed: I'd like to try, once more, seeing what it looks like for the uniform (non-axis-constrained) scaling to follow the cursor rather than sticking to the original angle when the scaling began. This should be a separate commit so it's easy to revert if the current behavior remains my preference.
• When resizing or rotating the transform cage, we'd like hints for cancel, Shift constrain aspect ratio (scaling the layer) or along axis (dragging the layer), Alt around the pivot (scaling the layer), and Ctrl snapping 15° increments (rotating the layer).