Adjust the formatting of date and next alarm time

Bug: 26014654
Bug: 26216446

The new chosen format matches the format displayed on the
marshmallow lock screen. Specifically, old format resembled:

Wed, February 3 ⏰ Thu 9:30 AM

while the new format resembles:

WED, FEB 3 ⏰ THU 9:30 AM

This change can be seen in the following locations:
- clock tab
- digital clock widget
- screensaver (invoked by long-pressing on clock tab)
- daydream (configured via Settings -> Display -> Daydream)

Change-Id: Ic86d5e85017940fdc809076425d326c8afcedd2b