There's about to be a second version that I'd like totest in parallel with the old version.

This is similar to SuppressedAssociatedTypes, but infersdefault requirements when primary associated types ofprotocols are suppressed. This defaulting for the primaryassociated types happens in extensions of the protocol,along with generic parameters, whenever a source-writtenrequirement states a conformance requirement for the protocol.Thus, the current scheme for this defaulting is a simplistic,driven by source-written requirements, rather than factsthat are inferred while building generic signatures.Defaults are not expanded for infinitely many associated types.Other changes include...Sema: adjust protocol extension signature hackWith SuppressedAssociatedTypesWithDefaults,we can have associated types that are missinginvertible conformance requirements, so we needto try re-building the signature for the extensionof the protocol. Otherwise, we won't infer the newdefault(s) for those associated types.This previous hack was only trying to shortcutthe rebuilding if it saw Self is lacking a conformancerequirement. Now it'll check if any inverses were writtenin source for that protocol.