[terra-folder-tree] Fix incorrect screenreader announcement of indexes

[sycombs]

Summary

This PR fixes an issue where screenreaders would announce subfolder items with sibling parents as being part of the same group. This has been done by manually setting the values for aria-setsize and aria-posinset instead of relying on browser calculations.

Testing

This change was tested using:

• WDIO
• Jest
• Visual testing (please attach a screenshot or recording)
• Other (please describe below)
• No tests are needed
  Tested with Voiceover and JAWS.

Reviews

In addition to engineering reviews, this PR needs:

• UX review
• Accessibility review
• Functional review

Additional Details

This PR resolves:

UXPLATFORM-10283

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[adoroshk]

I verified that while walking up/down the folder tree, it announces the level and item index in subset correctly. Looks like expected behavior.

[mjpalazzo]

@sycombs - I did some testing with JAWS with the basic folder tree example and it sounds like the issue is fixed. The levels and item index are announced correctly. I will do more testing with other examples.

[sdadn]

does this mean position in set? Can we rename this to positionInSet or itemPosition for clarity?

[sycombs]

I was torn between naming it posInSet, ariaPosInSet, or positionInSet as you suggested since this is a direct passthrough to aria-posinset. I'm not sure which is most appropriate - maybe ariaPosInSet since it matches the aria attribute?

[sdadn]

Oh if it's a direct passthrough, then yeah, ariaPosInSet sounds good!

[sycombs]

Updated both prop names: eccff30

[mjpalazzo]

@sycombs - here are some observations:
Folder Tree Selection example - The indexes are working correctly. Please regard my previous comment. I was in the wrong version.
Folder Tree Expand Collapse example - the level in the label and level JAWS announces do not match. The indexes start with 0 but the labels start with 1.
Folder Tree Expand Collapse All example - same comment.

[mjpalazzo]

@sycombs - here are some observations: Folder Tree Selection example - The indexes are working correctly. Please regard my previous comment. I was in the wrong version. Folder Tree Expand Collapse example - the level in the label and level JAWS announces do not match. The indexes start with 0 but the labels start with 1. Folder Tree Expand Collapse All example - same comment.

Great work, @sycombs! Those examples are much better and the component is working perfectly! I approved.