[digital-clock] Introduce new layouting state for small panels

One of the most reported bugs wrt digital clock is that the second line
text (date or timezone) is unreadable on small panels so this adds new
state to the clock applet that lays things horizontally when the panel
is too small to show text with the "small" font (set in system
settings).

When there is a date displayed, a delimiter is put in between to allow
easier and faster spotting the time (as on a first glance there is just
a bunch of numbers, so quickly orienteering is super important). I used
the dot symbol first but then went for pipe which I think looks more
clean.

REVIEW: 124449
CCBUG: 348072