SchemaMappingInspector enhancements

Support not only GraphQLObjectType, but any GraphQLFieldsContainer,
effectively also inspecting fields declared on an interface.

Add skipped types to report that includes any non-simple types that
have been skipped. Any type that is not a GraphQLFieldsContainer is
skipped, including unions. Types may also be skipped because of
insufficient Java object type information, e.g. controller method
declared to return Object or Mono<?>.

Do not report issues related to scalar and enum type fields, which
don't have any structure and don't need further checks.

See gh-662

Author: rstoyanchev

spring-graphql/src/main/java/org/springframework/graphql/execution/DefaultSchemaResourceGraphQlSourceBuilder.java

@@ -136,9 +136,7 @@ protected GraphQLSchema initGraphQlSchema() {
 		configureGraphQl(builder -> {
 			GraphQLSchema schema = builder.build().getGraphQLSchema();
 			SchemaMappingInspector.Report report = SchemaMappingInspector.inspect(schema, runtimeWiring);
-			if (!report.isEmpty()) {
-				logger.info(report.getSummary());
-			}
+			logger.info(report);
 		});
 
 		return (this.schemaFactory != null ?