[Editing] Update SelectionInDOMTree after inserting a node

This CL updates the `SelectionInDOMTree` on node insertion based
on the position of the inserted node, anchor and focus positions
of the `SelectionInDOMTree`. Currently the anchor or focus
positions are not updated when a node is inserted and the visible
selection and offset values in selection API (document.getSelection())
do not match after a node insertion.

Bug: 41329214
Change-Id: I27de5297e50460fce1b18831350c422f47c0fba2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5909161
Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Ashish Kumar <ashishkum@microsoft.com>
Reviewed-by: Siye Liu <siliu@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1388047}