Add tests for accessibility use cases

[BenHenning]

Check for duplicates

• I have searched for similar issues before opening a new one.

Problem

There aren't yet end-to-end tests for verifying the new keyboard navigation and accessibility use cases in Core Blockly (though they have started to be implemented for navigation in the keyboard navigation plugin repository: https://github.com/google/blockly-keyboard-experimentation/tree/main/test).

Request

WebdriverIO tests should be added that verify both keyboard navigation & readout state as more of the keyboard navigation plugin and navigation functionality is moved into Core Blockly.

Alternatives considered

No response

Additional context

No response

[BenHenning]

Reminder to consider shadow block cases specifically as they relate to selection & focus per #8916 (comment).