Add --start-app

Add a command line option --start-app=name to start an Android app by
its package name. For example:

    scrcpy --start-app=org.mozilla.firefox

The app will be started on the correct target display:

    scrcpy --new-display=1920x1080 --start-app=org.videolan.vlc

PR #5370 <https://github.com/Genymobile/scrcpy/pull/5370>

Co-authored-by: Simon Chan <1330321+yume-chan@users.noreply.github.com>