This CL fixes the issue where text runs after overlapping annotations
are not added to the accessibility tree. In the loop where text runs are
added to the accessibility tree, some text runs are skipped due to
incorrect normalization after overlapping annotations are added to the
tree.

Tests have been added to validate the scenario.

Fixed: 1066802
Change-Id: I6e7b3c72d9c25c45033a057d44261e888e9e7796
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2131808Reviewed-by: Kevin Babbitt <kbabbitt@microsoft.com>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Ankit Kumar 🌪️ <ankk@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#755928}