[api-digester] Teach the api-digester about hasMissingDesignatedInitializers

Because we won’t be serializing this attribute, add custom diagnostics for the cases where:

- We add @_hasMissingDesignatedInits to an open class, which means subclasses won’t be able to inherit its inits
- We remove @_inheritsConvenienceInitializers, which means APIs are removed

tools/swift-api-digester/ModuleDiagsConsumer.cpp

@@ -73,6 +73,8 @@ static StringRef getCategoryName(uint32_t ID) {
   case LocalDiagID::super_class_changed:
   case LocalDiagID::no_longer_open:
   case LocalDiagID::desig_init_added:
+  case LocalDiagID::added_invisible_designated_init:
+  case LocalDiagID::not_inheriting_convenience_inits:
     return "/* Class Inheritance Change */";
   default:
     return StringRef();