Confirm / finish keyboard moves on subsequent actions

[microbit-robert]

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Description

It is still possible to trigger other actions while a keyboard move is in progress leading to unexpected results or errors.

Moves are now confirmed when a user clicks outside of the workspace while a move is in progress (see #530). Other actions should probably follow suit and confirm the move before triggering the next action, this is supported by feedback we have received so far.

Scenarios that error while in move mode:

• Cut (Ctrl + X)
• Opening context menu (Ctrl + Enter)
• Clean up workspace (C) - no error but this can be confusing due to the amount of movement of other blocks

Other actions such as delete have checks in their precondition functions to avoid triggering the action. It would be good to align all of these to have the same behaviour with an approach that will also work for shortcuts added by apps using Blockly via the shortcut registry.

This PR suggests a couple of approaches to handling this problem, but there may well be other solutions.

Reproduction steps

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[microbit-robert]

The situation with being able to trigger other actions during a move has been temporarily made worse by the changes to delegate actions to core. E.g., you can now delete (and more) during a move and it ends badly.