Allow access to adapter (#634)

Currently there is no way to access the adapter outside of Vello, which
prevents users of Vello from doing things like checking surface
capabilities. This pull request exposes the adapter.

vello/src/util.rs

@@ -148,6 +148,13 @@ impl RenderContext {
     }
 }
 
+impl DeviceHandle {
+    /// Returns the adapter associated with the device.
+    pub fn adapter(&self) -> &Adapter {
+        &self.adapter
+    }
+}
+
 /// Combination of surface and its configuration.
 #[derive(Debug)]
 pub struct RenderSurface<'s> {