plugin: don't initialize the debounce plugin on a virtual device

Effectively the same motivation as commit 5d23794d53 ("tablet: disable
smoothing for uinput devices") - virtual devices should not need
debouncing and if they do let's do the debouncing on the other end that
creates those devices.

Part-of: <https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/1307>

src/libinput-plugin-button-debounce.c

@@ -34,6 +34,7 @@
 #include "libinput-log.h"
 #include "libinput-plugin-button-debounce.h"
 #include "libinput-plugin.h"
+#include "libinput-private.h"
 #include "libinput-util.h"
 #include "quirks.h"
 #include "timer.h"
@@ -755,6 +756,9 @@ debounce_plugin_device_added(struct libinput_plugin *libinput_plugin,
 	if (!libinput_device_has_capability(device, LIBINPUT_DEVICE_CAP_POINTER))
 		return;
 
+	if (libinput_device_is_virtual(device))
+		return;
+
 	_unref_(udev_device) *udev_device = libinput_device_get_udev_device(device);
 	if (udev_device) {
 		const char *prop = udev_device_get_property_value(udev_device,

src/libinput-private.h

@@ -730,6 +730,9 @@ libinput_device_init(struct libinput_device *device, struct libinput_seat *seat)
 bool
 libinput_device_has_model_quirk(struct libinput_device *device, enum quirk model_quirk);
 
+bool
+libinput_device_is_virtual(struct libinput_device *device);
+
 void
 libinput_device_disable_feature(struct libinput_device *device,
 				enum libinput_feature feature);

src/libinput.c

@@ -2252,6 +2252,12 @@ libinput_device_has_model_quirk(struct libinput_device *device, enum quirk model
 	return result;
 }
 
+bool
+libinput_device_is_virtual(struct libinput_device *device)
+{
+	return evdev_device_is_virtual((struct evdev_device *)device);
+}
+
 static uint32_t
 update_seat_key_count(struct libinput_seat *seat,
 		      keycode_t keycode,