This pr implements some parts of #1870 and also some minor improvements

• When using the path tool, R/S works about the anchor when a single handle is selected.
• When using the pen tool, Backspace/Delete removes the current segment's handle (equivalent to clicking the current anchor).

Minor improvements as discussed -

• G/R/S should have no effect (those keys should be ignored) while in the yellow point insertion sliding state - discord
• The global G/R/S is actually specific to the Select tool and Path tool - discord
• G/R/S when the selection is empty should, not activate G/R/S(A layer is selected but not any points in it. - discord
• Aborts from G/R/S when switching tools using hotkeys - discord