MR2ProviderServiceProxy: Change onBindingDied() behavior

When onBindingDied() is called, the current active connection
should be cleared. Also, internal states of the proxy such as
routes and sessions should also be cleared. Also, the Javadoc of
onBindingDied() says that we need to unbind and rebind in order to
activate the connection again.

Therefore, this CL makes the onBindingDied() unbind from the service
and rebind if necessary.

Bug: 198235819
Test: atest MediaRouter2Test#testTransferToSuccess --rerun-until-failure
      atest MediaRouter2Test#testTransferCallbackIsNotCalledAfterUnregistered
        --rerun-until-failure
      atest MediaRouter2Test --rerun-until-failure
Change-Id: I8c80a20b887bde9862f4936c42c99634cb22e352