Implement a11y tree mapping for ElementInternals element relationships.
Map element relationship properties (e.g. ariaLabelledByElements) set on ElementInternals through to the accessibility tree.
If the same property is set on both the element and its ElementInternals, properties set on the element take precedence.
Bug: 41469336
Change-Id: Ie5fca83aa647018b3f99454c51193e700a07fd5c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5836478
Reviewed-by: Aaron Leventhal aleventhal@chromium.org
Reviewed-by: Mason Freed masonf@chromium.org
Commit-Queue: Alice Boxhall alice@igalia.com
Cr-Commit-Position: refs/heads/main@{#1371181}