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/zsh-completion/_scrcpy

@@ -27,6 +27,7 @@ arguments=(
     '--force-adb-forward[Do not attempt to use \"adb reverse\" to connect to the device]'
     '--forward-all-clicks[Forward clicks to device]'
     {-h,--help}'[Print the help]'
+    '--kill-adb-on-close[Kill adb when scrcpy terminates]'
     {-K,--hid-keyboard}'[Simulate a physical keyboard by using HID over AOAv2]'
     '--legacy-paste[Inject computer clipboard text as a sequence of key events on Ctrl+v]'
     '--list-displays[List displays available on the device]'