Create a new badge drawable for feed header.

This is a 1-for-1 replacement of the existing unread dot drawable, allowing for addition of text and adjustment of size for later customizations.

Change-Id: Ida90c182d8efc742eef1284b9ac76f42e8b57445
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3717144


Reviewed-by: Peter Williamson <petewil@chromium.org>
Commit-Queue: Cathy Li <chili@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1026907}