Rename --encoder to --video-encoder

This prepares the introduction of --audio-encoder.

PR #3757 <https://github.com/Genymobile/scrcpy/pull/3757>

app/data/zsh-completion/_scrcpy

@@ -16,7 +16,6 @@ arguments=(
     '--display=[Specify the display id to mirror]'
     '--display-buffer=[Add a buffering delay \(in milliseconds\) before displaying]'
     {-e,--select-tcpip}'[Use TCP/IP device]'
-    '--encoder=[Use a specific MediaCodec encoder]'
     '--force-adb-forward[Do not attempt to use \"adb reverse\" to connect to the device]'
     '--forward-all-clicks[Forward clicks to device]'
     {-f,--fullscreen}'[Start in fullscreen]'
@@ -60,6 +59,7 @@ arguments=(
     {-v,--version}'[Print the version of scrcpy]'
     '--video-codec=[Select the video codec]:codec:(h264 h265 av1)'
     '--video-codec-options=[Set a list of comma-separated key\:type=value options for the device video encoder]'
+    '--video-encoder=[Use a specific MediaCodec video encoder]'
     {-w,--stay-awake}'[Keep the device on while scrcpy is running, when the device is plugged in]'
     '--window-borderless[Disable window decorations \(display borderless window\)]'
     '--window-title=[Set a custom window title]'