Allow equality checking and hash for HIDL interface proxies.

IFoo.Proxy.equals() -> HidlSupport.equals() ->
IHwInterface.asBinder().equals() -> HwRemoteBinder.equals().
IFoo.Stub.equals() -> default Object.equals()

Notice that IHwInterface.asBinder() returns mRemote(of type
HwRemoteBinder) for proxies and itself (of type HwBinder) for stubs.
If IFoo.Stub.asBinder() had not return "this", its equals()
should also be overridden.

Bug: 68727931
Test: hidl_test_java

Change-Id: I916983d7bc739747145e2ebb6830226310fd4980