Add --pause-on-exit

Add an option to make scrcpy pause on exit.

Three behaviors are possible:
 - always pause on exit:
    --pause-on-exit
    --pause-on-exit=true
 - never pause on exit:
    (no option)
    --pause-on-exit=false
 - pause when scrcpy returns with an error (a non-zero exit code):
    --pause-on-exit=if-error

This is useful to prevent the terminal window from automatically
closing, so that error messages can be read.

Refs #3817 <https://github.com/Genymobile/scrcpy/pull/3817>
Refs #3822 <https://github.com/Genymobile/scrcpy/pull/3822>
PR #4130 <https://github.com/Genymobile/scrcpy/pull/4130>