Restore the small ".4" fractional seconds display

that was lost when switching to a single TextView in order to make the
tapping style feedback span the entire time display.

This works by putting styled text into the TextView.
Improve some comments and isolate the possible RTL number formatting

in case RTL localizations need to put the fractional seconds before the
HHMMSS part. But defer getting the format string from the resources until
a L10N needs it. That requires complicating the TimeCounter's API since
it's the caller that can & should get string resources.