De-confuse InvocationHandler and target methods

De-confuse InvocationHandler and target methods

Having hashCode()/equals()/toString() implemented in InvocationHandler
could lead to confusing the handler with the object being proxied. It
furthermore violates equality contract requirement of being reflexive
-- the handler ends up being equal to other implementations of proxied
interface, but any other implementation would either have to handle
it specifically, or will determined it being non-equal.

Clean up the confusion by renaming the methods and have default
implementations take over. This is explicitly fine, as we do not have
any code accessing the handler directly, only through the proxy.
This also eliminates the need to suppress warnings.

Change-Id: Iac42d09b5a44716e8293c6b1e9003a780efae6f8
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
(cherry picked from commit 2cf87f876c50a276f6e5ddafc2fb44d5b6c26fbd)