multi-instance: Tweak the dialog paddings/margins to match the mock

Updates dialog UI xml definition to match the implementation to the
mock to dp level:
 - Instance item in window selector/move window
 - + New Window/max window info message
 - Back arrow icon in the confirmation dialog message
 - Globe icon tint adjusted to the current theme

Bug: 1245220
Change-Id: Ifbb58889d4fecc1b788f1ad57813a4b0e307dc42
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3132863


Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/main@{#918727}