Implement StructTree, improve accessibility

[MattL75]

@wojtekmaj Here is my rough proof-of-concept. I am having trouble getting Vitest to run. It seems to hang forever so I cannot run nor write unit tests at the moment :/

Adds accessible semantics to the canvas. Screen readers can now get great information for semantic elements such as lists.

Tested to work with Voiceover on mac.

[MattL75]

Still unsure why but downgrading Vitest to 0.28.5 allows me to run the tests.

[MattL75]

@wojtekmaj The only concern I have with this is the custom text renderer. There is no longer a direct mapping between textContent and the dom.

We could call getTextContent with the includeMarkedContent argument and only allow customization of the items which have a string attached.

What are your thoughts on this?

One option would be to look for the matching text in the DOM, though that would be much slower than the current implementation.

[MattL75]

Personally I feel this test is pointless now as there is no longer a direct mapping between customTextRender and normal.

[MattL75]

Solution to the customTextRenderer problem. No change of behaviour if you use a custom render function.

[wojtekmaj]

What's "customTextRenderer problem"? The fact one could render text items and remove some properties in the process?

[MattL75]

Well previously the custom text renderer had a 1-to-1 ratio of elements to text content. Now it's a bit different as the structure has more nested stuff within. I think the safest option is to just disable the accessibility layer if there is a custom renderer

[MattL75]

@wojtekmaj Any thoughts on this? :)

[wojtekmaj]

I refactored the code a bit to ensure type safety and to use useResolver which allows me to handle async loading more gracefully. I'm still not certain about a few things, please see my comments :)

[wojtekmaj]

TODO:

• Grow some brain and understand the includeMarkedContent/customTextRenderer issue deeply
• Document new callbacks
• Re-add relevant unit tests
• Figure out if StructTree is safe to render without text layer

[MattL75]

imo rendering struct tree without text layer is a bit pointless anyways. It could add a bit of context to some stuff like images. Honestly though if you're disabling the text layer you probably don't care much about making the document accessible

[wojtekmaj]

Not really about "care"/"not care" - but e.g. we have incoming #1519 :)

[wojtekmaj]

Phew, made it work in all cases, brought back the tests, everything looks pretty good in my opinion :D I know it's silly but can I ask YOU for a review now? 😂 Especially the screen reader with and without custom text renderer.

[wojtekmaj]

Let's goooo!