The basics

• I validated my changes

The details

Resolves

Fixes #9167
Fixes part of RaspberryPiFoundation/blockly-keyboard-experimentation#614

Proposed Changes

This PR adds support for keyboard navigation in and through workspace comments. Specifically, it:

• Factors out comment icons into their own classes that support being focused
• Adds navigation policies for workspace comments and icons
• Improves the Rect and WorkspaceSvg APIs to have better typings/additional convenience functions to support this

A (small) corresponding PR will still be needed in the keyboard-experimentation repo.

With this change, workspace comments are part of the keyboard nav flow; with a comment focused, Enter will focus its editor, Escape will return focus to the comment as a whole, and the collapse/delete icons may be reached by right-arrowing in from a focused workspace comment. Up and down include workspace comments as well as blocks in the list of locations that they visit.