Imply -q when stderr is not a tty

[binhdvo]

This avoids progress bar updates when inappropriate for stderr, to address #2816

[senhuang42]

The tests that fail here seem to be related to PR #2322. Changing the g_displayLevel is unfortunately fraught and the mechanisms for deciding what should be displayed are convoluted - if the tests failures are not descriptive enough, there's a good amount of discussion in #2322 for what the intended behavior should be, which might help with determining the correct fix for this.

[terrelln]

We should do this in the same place we handle quieting for stdout:

zstd/programs/zstdcli.c

Line 1405 in d7e1736

if (hasStdout && (g_displayLevel==2)) g_displayLevel=1;

I'm not sure if it would be better to move the stdout one up, or this one down though.

[Cyan4973]

-q implies disabling user prompt.
The existing displayLevel cutoff thresholds are correct.