Support multi-select polls

[bxdxnn]

I'm not a JavaScript/Web dev, please note that this PR is fully written by an LLM.

element-hq/element-meta#2694
element-hq/element-x-android#6477

Checklist

• I have read through review guidelines and CONTRIBUTING.md.
• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• I have licensed the changes to Element by completing the Contributor License Agreement (CLA)

[t3chguy]

How does this vary from #32681

Also needs test coverage

[bxdxnn]

How does this vary from #32681

Sorry for duplicating the work, I didn't check if there was already a PR for this.

This implementation is more consistent with the Android's implementation by using +/- buttons. The other PR seems to be simply using a text input.

A summary from an LLM:

Key Implementation Differences:

1. Max selections UI:

   • This PR uses +/- buttons with PlusIcon/MinusIcon for changing max selections
   • feat: support max_selections for multi-select polls #32681 uses a number input field

2. Edge case handling:

   • This PR: When adding/removing options, clamps maxSelections if it exceeds available options
   • feat: support max_selections for multi-select polls #32681: Doesn't adjust maxSelections when options change

3. Poll voting logic (MPollBody.tsx):

   • This PR: Tracks isVoting state to prevent double-clicks, uses local state for selection
   • feat: support max_selections for multi-select polls #32681: Relies on collectUserVotes to fetch user's existing votes

4. collectUserVotes function:

   • This PR: Updated signature to use array for selected parameter
   • feat: support max_selections for multi-select polls #32681: Original implementation with outdated documentation

5. CSS: Current branch adds new styles in _PollCreateDialog.pcss for the button-based UI

The current branch appears to be an evolution of the #32681 with improved UX (buttons vs input) and better handling of edge cases.

[t3chguy]

Needs design review, I suggest including some screenshots to make their lives easier

[t3chguy]

https://github.com/element-hq/element-web/blob/develop/CONTRIBUTING.md#:~:text=Please%20do%20not%20use%20force%20push%20in%20your%20PRs.%20Doing%20so%20means%20we%20can%27t%20see%20what%20has%20changed.%20We%20use%20squash%20merge%20to%20get%20a%20%22clean%22%20git%20history.

[mxandreas]

I checked this out quickly.

From visual design perspective, it looks "good enough" (considering it is more important to have this option than how aesthetic the configuration looks), but perhaps the + and - buttons should not be that much apart. cc @americanrefugee .

From functional point of view - if I created a poll with 2+ responses, I could still only vote for one. It did not seem like it was working.