[Editing] Fire selectionchange event on TextControl for backspace input

The selectionchange event does not get fired when the backspace key
deletes text inside a textcontrol element. According to the
specification [1], when an input or textarea element provide a text
selection and its selection changes (in either extent or direction),
the user agent must schedule a selectionchange event on the element.
This change ensures that the event will be scheduled as per the
specification.

[1] https://w3c.github.io/selection-api/#selectionchange-event

Bug: 41321247
Change-Id: Id6307b9baaee6480ba607ae8576959e2635e7b16
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6012498
Commit-Queue: Tanu Jain <tanujain@microsoft.com>
Reviewed-by: Siye Liu <siliu@microsoft.com>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1388005}