Integrating screen readers and keyboard navigation

[alschmiedt]

Is your feature request related to a problem? Please describe.
Should look at how keyboard navigation interacts with screen readers.

• Focus should go to toolbox when navigation opens the toolbox.
• How fields deal with focus
• Should loose focus when we click on something out of the workspace
  I am sure there are more I am just not aware of yet.

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Additional context

[BenHenning]

Note from RaspberryPiFoundation/blockly-keyboard-experimentation#523 (comment) that this work should include performing an NVDA test, particularly a page-level point-in-time analysis since our use of tabindexes is pretty complicated and could have unintended side effects.

This analysis should probably wait until more of the ARIA context is correct since that will presumably have a big impact on the context and how it's represented.