bug#39956: 26.2; improve display of information of M-x list-timers

[ndame]

I've been developing a package lately which uses several timers, and
because of that I use M-x list-timers often. I don't see in the NEWS of 27
changes related to this, so I list some problems.

The first thing which wasn't obvious first that the Next column displays
the time in seconds, but the Repeat column uses minutes, though it's
not indicated anywhere in the header that they use different units.

Generally, the best solution could be to use days, hours, minutes,
seconds format, instead of displaying floating point values.

E.g this line

             195.08     5.00 savehist-autosave

could be more readable like this

             3m 15.08s     5m  savehist-autosave


Or this one

       26479.43  1440.00 run-hooks

like this

       7h 21m 19.43s  1d run-hooks



The latter also demonstrates an other problem: if you only see
run-hooks as the function then you have no idea what will actually
run. It's not trivial to find the source. So if the function has args
then they should also be displayed, at least in some shortened form
with the too long part cut off if the args are too long.