Disable keyboard navigation looping

[gonfunko]

Currently, navigating through blocks with the keyboard will eventually reach the "end" of the workspace and loop around to the first block stack, forever. Instead, when the end is reached, navigation should stop and an audible cue should be emitted. The audio portion may require some experimentation and validation to identify an approach that is compatible/audible in conjunction with a screenreader.

[BenHenning]

Note that this changes the behavior for regular keyboard navigation users, too. I wonder if this necessitates adding jumping shortcuts for stack navigation or moving to the top/bottom stack of the workspace to allow for the same looping behavior to exist without it being default enabled.

[gonfunko]

See #9498 for the shortcuts :) My inclination here is to allow toggling looping on the LineCursor instance to keep backwards compatibility; then the keyboard experiment can just disable it, but we can keep the current behavior for other users, and if we decide we want it back it's just a method call away to revert.

[kmcnaught]

Just to flag that we didn't used to have looping on keyboard navigation, and it was a big confusion in user testing, particularly in ambiguous/confusing layouts like this (everyone pressed right arrow, nothing happened, and eventually most admitted defeat, possibly after trying down arrow to no avail too). Adding looping means that something always happens, so even if the ordering is a bit weird you get some feedback and find a way back to where you want.

[gonfunko]

Noted! With this layout and the current navigation right/down does navigate you to the next stack, even with looping turned off. The looping toggle is also effectively a one-liner, so this should be easy to revert if testing suggests that's needed or even if we want to vary the behavior contextually.