Changed the NotificationCenterBubble corner radius to 24px for Jelly

Before the change, both the NotificationListView and the
NotificationBubbleView has a corner radius of 16px. This CL changed the
bubble view's corner radius to be 24px for Jelly.

Screenshot:
https://screenshot.googleplex.com/7xzJaBCExs6pX5q

Bug: b:285024389
Change-Id: I5893b492e7b62bd44bdf2fd2d92c57525d134931
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4642262


Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Commit-Queue: Sylvie Liu <sylvieliu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1162681}