Fix ClassHelper::GetDirectInterface for proxy class

Returns only the direct interfaces implemented by the proxy class. We collect
them from the "interfaces" field in the synthesized proxy class instead of
looking into the iftable.

Also updates proxy_test to reflect this change.

Bug: 13689930
Change-Id: I926e2ed30f9e65972d700a378671cec82dedaa7c
2 files changed