tracking: Accessibility API

[Tropix126]

• Control over all accessibility node roles, properties, and flags.
  • Basic properties (string, bool, usize, enum) (feat: add attributes for most AccessKit properties #882)
  • Node associations (a11y_named_by, a11y_described_by, a11y_radio_group, etc...). Requires some sort of ID system (see below).
  • Control over screenreader actions.
    • Add builtin actions (this is internally a bitflag, maybe a11y_actions: "focus, blur, ...").
    • Add custom actions for screenreaders to announce. (not sure how to represent these as a string for attributes lol)
    • Respond to actions (requires a new event on nodes like onaccessibilityaction).
• Add some sort of ID system or similar for handling accessibility node associations.
• Measure inline text spans (word measurements, sentence measurements, etc...) and integrate them with AccessKit's APIs. Currently we just add a name property to label/paragraph elements with the inner text of the element, however the ideal way to do this is to have each text span be its own InlineTextBox accessibility node.
• Compute intrinsic AccessKit properties from existing attributes such as styles. (feat: infer accesskit properties from node state #855)
• Uncontrolled accessibility state (default accessibility state for nodes). (feat: Optional uncontrolled accessibility IDs #867)
• Incremental accessibility tree (avoid recreating the whole tree every render). (enhancement: Incremental Accessibility Tree #825)
• Improve focus handling.
  - [ ] onblur, onfocus events.
  • Filter non-focusable elements from tab order. (enhancement: Only focus focusable accessibility nodes #843)
  • Add and handle SetSequentialFocusNavigationStartingPoint and Blur actions for focusable nodes.
  • Focus-based keyboard events. (enhancement: Focus-based keyboard events #824)
  • Fix validation of focused element keyboard events (UseFocus::validate_globalkeydown only validates if keyboard focused. #883).
  • Uncontrolled NodeId generation without the need to use use_focus
  • Rename accessibility attributes so they have an a11y prefix. (feat: Rename a11y attributes #869)
  • a11y_autofocus (feat: a11y_auto_focus #878)
  • enhancement: Only focus focusable accessibility nodes #843
• Make freya_components accessible and at least on par with ARIA-compliant widgets.

I'm not fully up to date on the state IME support, but anything lacking in that area can also be thrown here.