Add RandomTranslation to serialization test (#1315)

* Add RandomTranslation to KerasCV

Let's keep this PR lightweight for now, then we can tidy the layer to
fit standards later.  Right now we are broken per Keras' latest release.

* Add copyright

* Lint fix

* Fix mixed precision test

* Fix random transltion layers

Author: LukeWood

keras_cv/layers/serialization_test.py

@@ -111,6 +111,11 @@ class SerializationTest(tf.test.TestCase, parameterized.TestCase):
             cv_layers.RandomChannelShift,
             {"value_range": (0, 255), "factor": 0.5},
         ),
+        (
+            "RandomTranslation",
+            cv_layers.RandomTranslation,
+            {"width_factor": (0, 0.5), "height_factor": 0.5},
+        ),
         (
             "Posterization",
             cv_layers.Posterization,