refactor: overhauled accessibility system via hook

[Tropix126]

Overhauls freya's accessibility APIs.

• Adds use_accessibility, which replaces and extends the previous use_focus hook. This gives the user access to most AccessKit NodeBuilder properties and flags.
• Removes existing accessibility attributes in favor of the hook.
• Attempts to derive as much data as possible from the node's styles to fill in accesskit properties.

TODO:

• [x] Implement an ActionHandler in Freya for handling commands from assistive technology.
• [ ] Expose a way for users to add actions to their accessibility nodes.
• [ ] Figure out inline text spans/measurement and how they play into this. Will be addressed later, need to hook skia text measurement APIs for that :/.
• [ ] Determine if AccessKit automatically infers properties such as position_in_set if unset. I know browsers do this, but it might be a different story here and we might have to do it ourselves (which would suck).
• [ ] Update components. This actually a HUGE undertaking if we want to do it right, and im leaning towards stripping out all accessibility from freya_components addressing this in future PRs, since the current state of accessibility in components is very incomplete or incorrect anyways.
• [ ] Update tests.
• [ ] Update examples.

[Tropix126]

Closing. This will be reimplemented in smaller PRs.