Chromium 133 support for source property and implicit anchor references

[chrisdavidmills]

Summary

Chrome 133 adds support for:

• The source option of the HTMLElement.showPopover() and HTMLElement.togglePopover() methods, which allow you to programmatically set the invoker (e.g. a button) of the popover the methods are being called on.
• New behavior whereby when you create an association between a popover and an invoker (using the above methods, or popovertarget/popoverTargetElement), an implicit anchor reference is created between the two, so they can be positioned via CSS anchor positioning.

This PR adds data points for the above.

Test results and supporting details

• ChromeStatus entry: https://chromestatus.com/feature/5120638407409664
• Spec PR: Add imperative access to popover invoker, and connect popover/invoker to implicit anchor element whatwg/html#10728
• MDN issue: Improvements to popover API and connection to anchor positioning mdn#598
• Associated MDN documentation: Editorial review: Document popover="hint" content#37990
• dom-example: Add popover=hint example dom-examples#295

I ran the example available in the above dom-examples PR in Chrome 133 release, and it works, which at least shows it is working by default in the lastest release, and is not behind a developer flag as the ChromeStatus seems to suggest.

Related issues

[Elchi3]

Looks good to me.

Heads up for @ddbeck that these new popover keys will affect the popover web-feature.