Refactor screencontrol to inputmanager

The "screen control" handled user input, which happened to be only
used to control the screen.

The controller and screen were passed to every function. Instead, group
them in a struct input_manager.

The purpose is to add a new shortcut to enable/disable FPS counter. This
feature is not related to "screen control", and will require access to
the "frames" instance.

app/meson.build

@@ -8,11 +8,11 @@ src = [
     'src/device.c',
     'src/fpscounter.c',
     'src/frames.c',
+    'src/inputmanager.c',
     'src/lockutil.c',
     'src/netutil.c',
     'src/scrcpy.c',
     'src/screen.c',
-    'src/screencontrol.c',
     'src/server.c',
     'src/strutil.c',
     'src/tinyxpm.c',