[NFC] Refactor DerivedConformances code to reduce diagnostics code duplication

[theblixguy]

This is a follow-up to #32797.

There was some code duplication for emitting new diagnostic notes for Comparable synthesis failures, so I have pulled the common code out for diagnosing derived conformance failures into separate functions which can be reused to emit the diagnostics.

1. diagnoseAnyNonConformingMemberTypes diagnoses any members of the conforming type that does not conform to the protocol we were trying to synthesise the conformance to. For example, Comparable synthesis requires the members of the conforming type to also be Comparable and using this method we can diagnose any members which does not conform to Comparable.

2. diagnoseIfSynthesisUnsupportedForDecl diagnoses the conforming type if we do not support derived conformances for that type. For example, Equatable synthesis is not supported for classes and using this method we can diagnose a given class type.

3. storedPropertiesNotConformingToProtocol returns any stored properties of a struct which do not conform to a given protocol. For example, diagnoseNonConformingMemberTypes uses this method to find the struct members which do not conform to the type for which we're trying to synthesise the conformance to. It is also used in canDeriveConformance to figure out if we can synthesise Equatable or Hashable for a struct.

[theblixguy]

@swift-ci please smoke test

[xedin]

👍