Ensure the Page chooser modal listing uses buttons

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• Use button not a (link) for the page chooser listing, select page buttons.
• Fixes Page chooser should use buttons instead of links with invalid targets #5408
• This was a small leftover goal from page editor rework and UX unification so just trying to get this sorted

Details

• Clean up some commented out css & also split out specific scss ignore lines in _listing.scss, the goal here being to clean up a little bit of this file but basically make the button look exactly the same as the a (link) variants used everywhere else.
• Add proper aria-description (intentionally not aria-label) to provide extra context for this button's purpose aria-description="{% trans "Select page" %}".
• Use classnames template tag for simpler classes generation.
• Note: The issue had an additional call out to change the way hover behaviour works (hover only on the clickable targets, I gave this a go but honestly the DOM structure & CSS here is pretty fragile and I opted for a smaller fix for the core issue before we start re-working everything.
• If this is merged, I will raise a new issue for the styling of the clickable buttons in page listings, we may want to add an explicit 'select' button (similar to full sized page listings) but this will require some additional thought.
• If this is merged, I will raise a new issue to adopt this solution for other chooser listings (images, document, snippets) along with the 'children' button.
  • wagtail/images/templates/wagtailimages/images/results.html
  • wagtail/images/templates/wagtailimages/chooser/results.html
  • Potentially others

Checklist

• Do the tests still pass?
• Does the code comply with the style guide?
• For front-end changes: Did you test on all of Wagtail’s supported environments?
  • Safari 15.4, Firefox 104, Chrome 105 including VoiceOver
  • Edge with NVDA

Screenshots

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Test this branch here: https://lb-fix5408-page-chooser-use-bu-kcw2u.squash.io

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Rebased

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Rebased

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Will close this for now, been over 6 months of rebasing / fixing conflicts - obviously not a big priority at this time. I will comment on the original issue that anyone is free to pick this up.