Add SF-operation to set array values

[t-b]

Use case:

• Replace ending time of epoch info with a fixed value

trange = [0, inf]
sel = select(channels(AD), sweeps())
dat = data($trange, $sel)
ep = epochs(E0, $sel)

setarray($ep, cols, [0 - 50], newValue)
setarray($ep, row, [0 - 50], newValue)
setarray($ep, row, *, newValue)

It would work on all datasets.

mop(setarray, could also be used to avoid polluting the namespace.