fix(popover): ensure arrow always points to trigger el

[averyjohnston]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Popovers with alignment="start" or "end" and arrow="true" position the arrow in the center of the popover. This can cause the arrow to fall outside the trigger element.

Issue URL: Resolves #24389

What is the new behavior?

For start and end alignments, the popover's arrow is positioned at the center of the trigger element instead. Popovers without a trigger element, such as those presented through a controller, are not affected.

Does this introduce a breaking change?

• Yes
• No

Other information

The difference is most obvious with small trigger elements, since those more easily cause the arrow to point at empty space.

Before	After

[averyjohnston]

WIP, still have a couple edge cases to account for.

[averyjohnston]

Closing after internal discussion. We decided to go with a simpler approach than this, since this fix adds a lot of complexity to fix a narrow subset of popovers. Will open a new PR soon, but I'll leave this up in case we decide to revisit.