Fix accessibility issue in creating shortcut.

When the Create Shortcut dialog is opened, the cursor
is at the start of the edit box and it is very hard to
move the cursor elsewhere while TalkBack is on.

The fix is to move the cursor to the end of the box
as soon as we populate the edit box.

Bug: 330450844
Change-Id: I3dfc7f533e51e2843c32f27f40fcc8d31171fb53
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5381561
Reviewed-by: Glenn Hartmann <hartmanng@chromium.org>
Commit-Queue: Finnur Thorarinsson <finnur@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1275572}