Move SimpleDigitalClockTextView to shared lib

This also updates our naming convention for some of these classes to
better match their current intention. The updated names will also help
avoid confusion with overlapping names as we migrate the existing clocks
to use this common code instead of the duplicated versions.

Bug: 364680879
Flag: NONE Library Refactor
Test: Checked functions of existing clocks
Change-Id: Iccf6264ac416a78f457414960281eda7e2b99c9a