Add --audio-dup

Add an option to duplicate audio on the device, compatible with the new
audio playback capture (--audio-source=playback).

Fixes #3875 <https://github.com/Genymobile/scrcpy/issues/3875>
Fixes #4380 <https://github.com/Genymobile/scrcpy/issues/4380>
PR #5102 <https://github.com/Genymobile/scrcpy/pull/5102>

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

app/data/bash-completion/scrcpy

@@ -6,6 +6,7 @@ _scrcpy() {
         --audio-buffer=
         --audio-codec=
         --audio-codec-options=
+        --audio-dup
         --audio-encoder=
         --audio-source=
         --audio-output-buffer=