Add AtkText support for caret methods and events

Bug: 866338
Change-Id: I5edb2c94b8ebd0807fec081c593188cbbb672801
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1486231
Commit-Queue: Martin Robinson <mrobinson@igalia.com>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#639046}
9 files changed