The way BatchLoaderHandlerMethod resolve argument

[dugenkui03]

In #232 , I suggested that @BatchMapping should support @Argument, because user will define arguments on field, no matter whether the field is fetched by DataLoader or 'n+1' way. Furthermore, user will always want to get information about field, such as field definition or directives info.

Hence, I think BatchLoaderHandlerMethod should support custom argument resolve strategy which resolving method parameters into argument values, like #295 . BatchMappingDataFetcher should use dataLoader.load(env.getSource(), env);(code like below), and argument resolve strategy and batch handler method will get all the information about the fetched field.

	static class BatchMappingDataFetcher implements DataFetcher<Object> {

                ......

		@Override
		public Object get(DataFetchingEnvironment env) {
			DataLoader<?, ?> dataLoader = env.getDataLoaderRegistry().getDataLoader(this.dataLoaderKey);
			if (dataLoader == null) {
				throw new IllegalStateException("No DataLoader for key '" + this.dataLoaderKey + "'");
			}
                         // pass DataFetchingEnvironment to DataLoader and other component
			return dataLoader.load(env.getSource(), env);
		}
	}

[dugenkui03]

#298 This pr support for BatchHandlerMethodArgumentResolver. Maybe a later pr could custom BatchHandlerMethodArgumentResolver (similar like #295). Is this a right way

[dugenkui03]

Details in #298