Add and position blocks from toolbox with keyboard

[tracygardner]

Make adding, placing and editing blocks from the toolbox fully accessible and intuitive with keyboard controls.

• Expand subcategories when you navigate to them with the keyboard (they auto expand when you click/tap)
• Esc should close flyout (and return focus to Toolbox category if that's where it came from)
• Toolbox visual highlights are unclear
• Scrollbar appears on toolbox, can we avoid this
• Colour grid input editor is not selected if current colour is not a grid option - you can Tab to the container but it's not easily discoverable
• When cursor it outside of view, workspace doesn't scroll when block is added - review more generally to find broken scenarios

[tracygardner]

Expand subcategories on keyboard focus to make them discoverable.

1bc5c06

[lawsie]

👍