Accessibility: Read the time correctly in quick settings.

The problem is that, for 12-hour locales, we cut the "a"
part of the time format out to show it in a separate
TextView so it can be animated independently of the actual
time. Unfortunately, while TTS is smart enough to pronounce
"1:15 AM" as /wʌn fɪftin eɪ ɛm/, "AM" on its own looks like
the English word "am" and is pronounced /æm/.

To fix this, a TextClock must be able to accept separate
formats for its content description than its presentation.
With this capability we can place the complete 12-hour time
format (including am/pm) in one of the views and suppress
the other one, so that the utterance creates an identical
experience to visual inspection: "1:15 AM" for all users.

Bug: 21718000
Change-Id: Ic9920d71ae4d4ad41ba86d7bd96f9a19b07e2108