binder: Add RpcCertificateVerifier.

An interface with a function that verifies a peer certificate.
It is a wrapper over the custom
verify function (see SSL_CTX_set_custom_verify).

Also, RpcTransportCtxFactoryTls::make() requests
an RpcCertificateVerifier.

Bug: 198833574
Test: binderRpcTest
Change-Id: I6e63bc84ede07735baaf8e02fda53a97775c3dcc