Rename Drawable Part/Segment/Point to DrawablePart/Segment/Point.

This way we don't have to prepend `NotificationProgressDrawable.` to them
in order to distinguish from the view types with the same names.

Compared to alternative options for renaming, this renaming aligns best
with existing names of variables etc.

Also applied some reformatting changes.

Flag: android.app.api_rich_ongoing
Bug: 372908709
Test: NotificationProgressBarTest
Test: Post ProgressStyle notifs via test app
Test: patch ag/30006048 and run ProgressStyleNotificationScreenshotTest
Change-Id: Id80d378d91478d7b5987579ac2faed5780f7c3ee