fix: Improve display of move-related hints

[gonfunko]

The basics

• I validated my changes

The details

Resolves

Fixes #9799

Proposed Changes

This PR improves the display of move mode-related hints in toasts. Specifically, it:

• Displays a prompt to use unconstrained mode every time the arrow keys are used without a modifier when the block being moved has no available destinations
• Displays a prompt to use constrained/unconstrained move mode, as appropriate, the first time a block is inserted from the flyout as does/does not have available destinations.