Look at method args and return types when looking for deps

Dependencies can appear only through method arguments or return types.
This makes sure they are taken into account when computing all the
dependencies for a given class.

Bug: N/A
Test: layoutlib tests
Change-Id: Id28d423cc1e1aae4428f9b443ea000808006eca0
(cherry picked from commit f53af782c135f254a449e5c46f290695e08ba06a)