Support for BatchHandlerMethodArgumentResolver

[dugenkui03]

The purpose of this PR

Replace hard code in BatchLoaderHandlerMethod with BatchHandlerMethodArgumentResolver, and support custom BatchHandlerMethodArgumentResolver.

1、Why spring-graphql should support BatchHandlerMethodArgumentResolver

User will define arguments on field, no matter whether the field is fetched by DataLoader or fetched directly( n+1 way). And user will always want to get additional information about field, such as Directives, FieldDefinition.

In conclusion, we'd better suport pass all the information of DataFetchingEnvironment to batch handler method. That said BatchLoaderHandlerMethod should support argumentResolve strategies which resolving argument values into various method parameters, and developers could custom their BatchLoaderHandlerMethod.

2、The way spring-graphql support BatchHandlerMethodArgumentResolver

Replace dataLoader.load(env.getSource()) with dataLoader.load(env.getSource(), env).

	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);
		}
	}

Brief change log

• replace BatchLoaderHandlerMethod#resolveArgument with BatchHandlerMethodArgumentResolver, and support custom BatchLoaderHandlerMethod ;
• add strategies: ArgumentBatchMethodArgumentResolver、ArgumentMapBatchMethodArgumentResolver、ArgumentsBatchMethodArgumentResolver and update document;
• support for validate batchHandlerMethod input;
• add unit tests for new batch method argument resolve strategies and the capability of custom BatchHandlerMethodArgumentResolver.