Make togglePopover throw more exceptions

[josepharhar]

This PR makes sure that togglePopover will throw exceptions when it is disconnected from the document or doesn't have a popover attribute.

Fixes #8999

• At least two implementers are interested (and none opposed):
  • Chrome
  • Safari
• Tests are written and can be reviewed and commented upon at:
  • Make togglePopover throw more exceptions web-platform-tests/wpt#40682
• Implementation bugs are filed:
  • Chromium: https://chromium-review.googlesource.com/c/chromium/src/+/4634324
  • Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=1840855
  • WebKit: https://bugs.webkit.org/show_bug.cgi?id=258574
• MDN issue is filed: imo this case doesn't need to be documented in MDN

(See WHATWG Working Mode: Changes for more details.)

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/popover.html ( diff )

[nt1m]

Looks ok to me, @annevk what do you think?

[annevk]

Seems reasonable and thanks for addressing! Please complete the checkboxes in OP and address the nit.

[nt1m]

(there's already a WebKit bug so no need to file one: https://bugs.webkit.org/show_bug.cgi?id=258574)

[josepharhar]

Please complete the checkboxes in OP and address the nit.

done