There is no frame rate to count.

Add the possibility to solely control the device without screen
mirroring:

    scrcpy --no-video --no-audio

This is different from OTG mode, which does not require USB debugging at
all. Here, the standard mode is used but with the possibility to disable
video playback.

By default, always open a window (even without video playback), and add
an option --no-window.

Fixes #4727 <#4727>
Fixes #4793 <#4793>
PR #4868 <#4868>

PR #4868 <#4868>

This is particularly important to react to server socket disconnection
since video and audio may be disabled.

PR #4868 <#4868>