ARIA for text input fields

[rachel-fenichel]

See the parent issue #8205 for more information about the general problem.

This issue is for discussing and agreeing on expected behaviour, and then tracking implementation.

Tasks:

• Apply the correct ARIA roles and properties to the DOM elements that represent the field
• Provide accessible names and descriptions to the DOM elements that represent the field
• Make sure the field works both during editing and during display (not editing)
• Describe the correct keyboard shortcuts to move into and out of editing mode when on a single instance of the field (e.g. enter, space, and esc)
  • Implementation may happen in the keyboard nav code or repository

Resources:

• ARIA: textbox role
• Blockly text input field documentation