Migrating lookup functions and predicates into API modules

[Cantor, Scott]

FYI, I'm going to correct a mistake and move a lot of the various lookup
functions and predicates in the impl modules up into the API. I realized
that there will be cases where people are supposed to use them to
implement conditions to control various things (resolver conditionals,
relying party lookup, signing/encryption, etc.) and they may have to
specify them by class in some cases, so the class names need to be
public/stable for upgrades.

-- Scott