Try to clarify which scrollbar setting is for what

The scrollbar setting in the Tools tab isn't about the canvas
scrollbar, but about the scrollbars in dockers and popups that
have a resource selector.

The scrollbar setting in the Display Page, misc tab is about the
canvas scrollbars.

BUG:413221
(cherry picked from commit 9e6c91fe34d1f2ff1fce582ff361d301a2d70985)