Move the filterNonDocumented and filterNonPublic functions as extension getters

[srawlins]

filterNonPublic becomes an extension getter, wherePublic, and filterNonDocumented becomes an extension getter, whereDocumented.

Nameable now implements Privacy. Privacy is now an abstract interface class.

Changing all the call sites highlights a number of ModelElement getters that are superfluous. For example, Container.publicInstanceMethods. This was a getter that now boils down to instanceMethods.wherePublic, and it really is unneccessary to keep this; there are many such methods that are removed here:

• Container: publicInstanceMethods, publicInstanceOperators, publicInstanceFields, publicConstantFields,
• InheritingContainer: publicSuperChain, publicInheritedFields, publicInheritedMethods,
• LibraryContainer: publicLibraries,
• Package: documentedCategories,
• PackageGraph: documentedExtensions,
• TopLevelContainer: publicClasses, publicExtensions, publicExtensionTypes, publicConstants, publicEnums, _publicExceptions, publicFunctions, publicMixins, publicProperties, publicTypedefs.

Additionally, this change highlights some small inefficiency in some hasX methods. For example, hasPublicInstanceMethods used to enumerate all of the public instance methods, then ask if the list is empty. Now we can ask if any of the instanceMethods are public.

• Container: hasPublicInstanceMethods, hasPublicInstanceOperators, hasPublicInstanceFields, hasPublicConstantFields, hasPublicVariableStaticFields, hasPublicStaticMethods, hasPublicEnumValues,
• InheritingContainer: hasPublicInheritedMethods, hasPublicSuperChainReversed,
• MixedInTypes: hasPublicMixedInTypes,
• LibraryContainer: hasPublicLibraries,
• Package: hasDocumentedCategories,
• TopLevelContainer: hasPublicClasses, hasPublicExtensions, hasPublicExtensionTypes, hasPublicConstants, hasPublicEnums, hasPublicExceptions, hasPublicFunctions,hasPublicMixins, hasPublicProperties, hasPublicTypedefs.

Because the field InheritingContaier.publicSuperChain is removed, I change superChain from a getter to a field, sort of the point of caching.

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