vulkan: move OnDrop out of vulkan module

src/utils/on_drop.rs

@@ -0,0 +1,17 @@
+use std::mem;
+
+pub struct OnDrop<F>(pub F)
+where
+    F: FnMut() + Copy;
+
+impl<F: FnMut() + Copy> OnDrop<F> {
+    pub fn forget(self) {
+        mem::forget(self);
+    }
+}
+
+impl<F: FnMut() + Copy> Drop for OnDrop<F> {
+    fn drop(&mut self) {
+        (self.0)();
+    }
+}