[ntp composebox] Set up clear and submit buttons

Add clear and submit buttons including colors for the buttons,
svgs of the submit button, and functionality to close the composebox.

Submit Disabled: http://screenshot/36iTg67MPzHHchj
Submit Enabled: http://screenshot/Ap56dqb9cGduoKD

NO_IFTTT=Changes are in both files.

Bug: 421960546, 420678349
Change-Id: I51b62321f5a0ecac41631491fd7de5183cb0037d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6631082
Reviewed-by: Riley Tatum <rtatum@google.com>
Commit-Queue: Marlon Facey <mfacey@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1474737}