Gate popover handling

[joedolson]

Implement a check for popover, and if not available, hide popover panel.

Prevents errors from the potentially invalid selector :popover-open and prevents uncloseable panels.

Not yet tested in a browser that doesn't support popovers, so this is currently hypothetical.

Trac ticket: https://core.trac.wordpress.org/ticket/65943

Use of AI Tools

None

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props joedolson, adamsilverstein.

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[github-actions]

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[adamsilverstein]

Excellent!

[adamsilverstein]

Nice one @joedolson - feel free to proceed if you want to get this in by 7.1.1 (RC on Sept. 10th).

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 63543
GitHub commit: 3e181d3

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.

[adamsilverstein]

I installed an older version of firefox and verified the issue as well as the fix in this PR:

Check:

Before:

After: