revisit PRs touching on posinset, setsize, level

[pkra]

Following last week's discussion I spotted more work open PRs related to this. I tried to find all open pull requests:

• Update: fix inconsistency around aria-setsize=-1 #2341
• Update: option element mapping table #2365
• [html-aam PR 540] Clarify li element role mapping #2212 (comment)
• Adds support for posinset/setsize in toolbars #2170
• Add normative text on calculating aria-level, aria-posinset, and aria-setsize #2104
• Allow treeitems to omit groups by specifiying aria-level, aria-posinset, and aria-setsize #2091

It seems we might need to coordinate some of these