Local means do not build streamer info for bases.
Improve error message.
Survive and signal non-unique lookup results.
Survive lookup in a forward declared context.
Use cling::utils::Lookup::Named().

Iterating through all functions is considerably slower than a lookup; as a side-
effect it also deserialized all methods. TMetaUtils::ClassInfo__HasMethod() now
returns what it has found - though that can still be -1 signaling "multiple
overloads."

Reduce he requirements of TMetaUtils::ClassInfo__HasMethod() such that it can now
also be used by rootcling's Namespace__HasMethod.
Simplify; use ROOT::TMetaUtils::ClassInfo__HasMethod().
Use TMetaUtils::GetClassVersion() instead of code dupe.
Skip offsets for classes with custom streamer or collection proxy.