Add PopoverAnchorRelationships flag and basic imperative API
This adds the PopoverAnchorRelationships feature flag, and
updates the IDL to add options bags to the relevant popover
APIs.
Chromestatus:
https://chromestatus.com/feature/5120638407409664
Bug: 364669918
Change-Id: I30cd45ff2a1f184e9e1b56b4cef7c5dc8e7557dc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5837806
Auto-Submit: Mason Freed masonf@chromium.org
Commit-Queue: Mason Freed masonf@chromium.org
Reviewed-by: David Baron dbaron@chromium.org
Cr-Commit-Position: refs/heads/main@{#1353062}