feat: Add verbosity shortcuts (experimental)

[BenHenning]

The basics

• I validated my changes

The details

Resolves

Fixes part of RaspberryPiFoundation/blockly-keyboard-experimentation#764
Fixes part of #9450 (infrastructure needs)

Proposed Changes

Introduces support for two new "where am I?" shortcuts for helping to provide location context for users:

• I: re-reads the current selected block with full verbosity (i.e. also includes the block's field types with their values in the readout).
• shift+I: reads the current selected block's parent with full verbosity.

Note that this includes some functional changes to Field to allow for more powerful customization of a field's ARIA representation (by splitting up value and type), though a field's value defaults potentially to null which will be ignored in the final ARIA computed label. This seems necessary per the discussion here: https://github.com/RaspberryPiFoundation/blockly/pull/9470/files#r2541508565 but more consideration may be needed here as part of #9307.

Some limitations in the new shortcuts:

• They will not read out anything if a block is not selected (e.g. for fields and icons).
• They read out input blocks when the input block is selected.
• They cannot read out anything while in move mode (due to the behavior here in the plugin which automatically cancels moves if an unknown shortcut is pressed: https://github.com/RaspberryPiFoundation/blockly-keyboard-experimentation/blob/a36f3662b05c2ddcd18bde8745777fff8dc3df31/src/actions/mover.ts#L166-L191).
• The readout is limited by the problems of dynamic ARIA announcements (per [Screen reader] Review of aria-live region announcements #9460).

Reason for Changes

RaspberryPiFoundation/blockly-keyboard-experimentation#764 provides context on the specific needs addressed here.

Test Coverage

Self tested. No new automated tests needed for experimental work.

Documentation

No new documentation needed for experimental work.

Additional Information

This was spun out of #9470 with the intent of getting shortcuts initially working checked in even if the entirety of the experience is incomplete.

[BenHenning]

Quick self-review spot check.

[BenHenning]

Post-conflict merge spot check.

[BenHenning]

PTAL @maribethb. I'm not considering this a full completion of RaspberryPiFoundation/blockly-keyboard-experimentation#764 for the caveats listed in the PR description, but it seems perhaps reasonable to check this in as-is and iterate to address the remaining needs of the issue (which may require changes both here & in the plugin).

Note I'll also revisit #9470 after this is merged since that's lower priority (and duplicates some of the code here so it's easier to pipeline it).

At least 2 of the 4 WebdriverIO failures on Mac seem to be existing. The other 2 look a bit different, but I don't think this is actually a new failure since the Linux tests aren't failing (and I'd expect them to in such a case).

[BenHenning]

/cc @microbit-robert for FYI.