types/wlr_input_device: move init and finish function to private API

include/interfaces/wlr_input_device.h

@@ -0,0 +1,20 @@
+#ifndef INTERFACES_INPUT_DEVICE_H
+#define INTERFACES_INPUT_DEVICE_H
+
+#include <wlr/types/wlr_input_device.h>
+
+/**
+ * Initializes a given wlr_input_device. Allocates memory for the name and sets
+ * its vendor and product id to 0.
+ * wlr_device must be non-NULL.
+ */
+void wlr_input_device_init(struct wlr_input_device *wlr_device,
+	enum wlr_input_device_type type, const char *name);
+
+/**
+ * Cleans up all the memory owned by a given wlr_input_device and signals
+ * the destroy event.
+ */
+void wlr_input_device_finish(struct wlr_input_device *wlr_device);
+
+#endif