Use computer's mouse to control Android device without mirroring and without losing control of your PC (like second display)

- [x] I have checked that a similar [feature request](https://github.com/Genymobile/scrcpy/issues?q=is%3Aopen+is%3Aissue+label%3A%22feature+request%22) does not already exist.

I found a few issues related to using scrcpy as a second display (i.e. inverting scrcpy), but that's not quite what I need.

My tablet sits next to my monitor. And sometimes I need to use it.
I want to move the mouse cursor to it as if it were a second monitor. But not translate the windows screen to it, but just let me control the tablet itself.

Similarly with the keyboard.

Scrcpy actually has everything for this, but you need to tell the system that a second monitor has been connected.

Start by reviewing scrcpy's existing mouse and keyboard control behavior and its interaction with the host window system; the issue names no files or tests. Define how input should reach the Android device without mirroring or taking control of the PC, then verify the behavior on the described second-display setup.

Written by the indexing model from the issue text.