Add option to kill adb on close

Killing adb on close by default would be incorrect, since it would break
any other usage of adb in parallel.

It could be easily done manually by calling "adb kill-server" once
scrcpy terminates, but add an option --kill-adb-on-close for
convenience.

Fixes #205 <https://github.com/Genymobile/scrcpy/issues/205>
Fixes #2580 <https://github.com/Genymobile/scrcpy/issues/2580>
Fixes #4049 <https://github.com/Genymobile/scrcpy/issues/4049>

app/data/bash-completion/scrcpy

@@ -20,6 +20,7 @@ _scrcpy() {
         --force-adb-forward
         --forward-all-clicks
         -h --help
+        --kill-adb-on-close
         -K --hid-keyboard
         --legacy-paste
         --list-displays