Unable to move AMP story block using keyboard

[spacedmonkey]

Bug Description

When using keyboard navigation, users are unable to move movable blocks in the AMP Story interface. For accessible reasons, this should be possible.

Expected Behaviour

Steps to reproduce

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Screenshots

Additional context

• WordPress version:
• Plugin version:
• Gutenberg plugin version (if applicable):
• AMP plugin template mode:
• PHP version:
• OS:
• Browser: [e.g. chrome, safari]
• Device: [e.g. iPhone6]

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Acceptance criteria

• After selecting a block, I should be able to move the block up, down, left and right via the direction keys. (QUESTION: HOW MUCH SHOULD IT MOVE ON EACH KEY STROKE?)

Implementation brief

QA testing instructions

Demo

Changelog entry

[barklund]

It's not trivial, but here's a great guide to best practice expected behaviour.

[swissspidy]

Previously suggested in #2454. Will close it as a duplicate.

[spacedmonkey]

As a talking point, I have created a WIP pull request in #3400. It is still discovery stages at this point, but it is a workable solution.

[spacedmonkey]

Screencast of the tabbing and arrows in use.
https://www.youtube.com/watch?v=u280hGEgCd0&feature=youtu.be

[spacedmonkey]

@MackenzieHartung @pbakaus A lot of work and discussion has taken place on #3400 . This ticket is not just a simple bug, it has lots of moving parts and is a fundamental change on how blocks are moved. This PR will effect other on going such as #3060 #3311 #3416 . This ticket needs to go through the new process, so we can capture all requirements

[jauyong]

Hey @jasti I only added the one AC for now. Based on @spacedmonkey's comments I'm not sure if that is too high level and if more is needed. I will wait for you to move this to the IB column...

[swissspidy]

In #3400 I left a comment for a new feature that could be its own AC:

It would be nice if one could move in bigger steps when holding down an additional key, e.g. ctrl, alt, or cmd. If I am not mistaken this kind of behavior is common in other applications when moving elements with the keyboard.

So just arrow keys: move by single pixels
Meta key + arrow key: move in steps of N pixels