Use device id 0 for touch/mouse events

Virtual device is only for keyboard sources, not mouse or touchscreen
sources. Here is the value of InputDevice.getDevice(-1).toString():

    Input Device -1: Virtual
      Descriptor: ...
      Generation: 2
      Location: built-in
      Keyboard Type: alphabetic
      Has Vibrator: false
      Has mic: false
      Sources: 0x301 ( keyboard dpad )

InputDevice.getDeviceId() documentation says:

> An id of zero indicates that the event didn't come from a physical
> device and maps to the default keymap.

<https://developer.android.com/reference/android/view/InputEvent#getDeviceId()>

However, injecting events with a device id of 0 causes event.getDevice()
to be null on the client-side.

Commit 26529d37 used -1 as a workaround
to avoid a NPE on a specific Android TV device. But this is a bug in the
device system, which wrongly assumes that input device may not be null.

A similar issue was present in Flutter, but it is now fixed:
 - <https://github.com/flutter/flutter/issues/30665>
 - <https://github.com/flutter/engine/pull/7986>

On the other hand, using an id of -1 for touchscreen events (which is
invalid) causes issues for some apps:
<https://github.com/Genymobile/scrcpy/issues/2125#issuecomment-790535792>

Therefore, use a device id of 0.

An alternative could be to find an existing device matching the source,
like "adb shell input" does. See getInputDeviceId():
<https://android.googlesource.com/platform/frameworks/base.git/+/master/cmds/input/src/com/android/commands/input/Input.java>

But it seems better to indicate that the event didn't come from a
physical device, and it would not solve #962 anyway, because an Android
TV has no touchscreen.

Refs #962 <https://github.com/Genymobile/scrcpy/issues/962>
Fixes #2125 <https://github.com/Genymobile/scrcpy/issues/2125>

server/src/main/java/com/genymobile/scrcpy/Controller.java

@@ -14,7 +14,7 @@ import java.util.concurrent.TimeUnit;
 
 public class Controller {
 
-    private static final int DEVICE_ID_VIRTUAL = -1;
+    private static final int DEFAULT_DEVICE_ID = 0;
 
     private static final ScheduledExecutorService EXECUTOR = Executors.newSingleThreadScheduledExecutor();
 
@@ -210,7 +210,7 @@ public class Controller {
         int source = nonPrimaryButtonPressed ? InputDevice.SOURCE_MOUSE : InputDevice.SOURCE_TOUCHSCREEN;
 
         MotionEvent event = MotionEvent
-                .obtain(lastTouchDown, now, action, pointerCount, pointerProperties, pointerCoords, 0, buttons, 1f, 1f, DEVICE_ID_VIRTUAL, 0, source,
+                .obtain(lastTouchDown, now, action, pointerCount, pointerProperties, pointerCoords, 0, buttons, 1f, 1f, DEFAULT_DEVICE_ID, 0, source,
                         0);
         return device.injectEvent(event);
     }
@@ -233,7 +233,7 @@ public class Controller {
         coords.setAxisValue(MotionEvent.AXIS_VSCROLL, vScroll);
 
         MotionEvent event = MotionEvent
-                .obtain(lastTouchDown, now, MotionEvent.ACTION_SCROLL, 1, pointerProperties, pointerCoords, 0, 0, 1f, 1f, DEVICE_ID_VIRTUAL, 0,
+                .obtain(lastTouchDown, now, MotionEvent.ACTION_SCROLL, 1, pointerProperties, pointerCoords, 0, 0, 1f, 1f, DEFAULT_DEVICE_ID, 0,
                         InputDevice.SOURCE_TOUCHSCREEN, 0);
         return device.injectEvent(event);
     }