Tweak UI of UsageProgressBarPreference

- Number in usage summary shows font of size 64.
- Usage summary uses sans font.
- Remove width percentage design.
- Change top/bottom padding from 32 to 16.
- Remove margin between summary text and progress bar.

Bug: 177617478
Test: manual visual
Change-Id: I8e19d98b03226828959be57ed2c0c21a90a88f81