feat: Add new Popover utility component

[kurtdoherty]

Context

• The existing Menu component is partially complete, but has a number of issues related to it (focus outline of items is clipped, menu item prop interface incomplete, inadequate positioning w.r.t anchor, reliant on div container which interferes with the layout of the trigger and more)
• We need to deliver a more solid foundation for Menu's while also supporting the updated Menu design requirements.
• To do this, we'll deprecate the existing Menu and implement a new one. This will allow consumers (including other Elements components) to gradually migrate to the new version.
• Previous work in this series:
  • chore: Deprecate existing Menu #636
  • feat: Add new MenuItem and AnchorMenuItem components #637
  • feat: Add new MenuGroup component #640

This PR

• Adds new Popover component. This will for the foundation of the new Menu component (and later, the Tooltip).

[rpt-uk-github]

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[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for d0c14141	✅ 100.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (d0c1414)	Report Missing	Report Missing	Report Missing
Head commit (707aacc)	7993	7269	90.94%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#641)	119	119	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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Footnotes

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[kurtdoherty]

note: small scout to use a more standard approach to CSS feature detection. The original method used here was take from the polyfill's examples.

[kurtdoherty]

note: as the JS Doc highlights below, this is a (temporary) function that will help consumers avoid the use of @ts-expect-error (or worse, @ts-ignore) every time they wire up a trigger with a popover-based component.

[kurtdoherty]

note: applyCSSAnchorPositioningPolyfill will conditionally apply the polyfill, so there's no need to check for support here.