TranslationResponseValue: Override equals() behaviour for Extras.

Bundle doesn't override equals(). In TranslationResponseValue, the
Extras is used as a simple value type, so contents can be compared.

Bundle.kindofEquals probably works here, but this change just makes it
work for empty bundles for now, to fix a bug in animation.

Bug: 144292180
Test: atest CtsTranslationTestCases
Change-Id: I68daac8cafceb1aa446ee89ba1405595b22e6213