Revise implementation to support multiple field projection, by names

[github-actions]

Revise implementation to support multiple field projection, by names

and indexes.

https://github.com/apache/incubator-wayang/blob/3fa657bcc8c86198b9532aa06bf27964c3f771be/wayang-commons/wayang-basic/src/main/java/org/apache/wayang/basic/function/ProjectionDescriptor.java#L41

package org.apache.wayang.basic.function;

import java.lang.reflect.Field;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

import org.apache.wayang.basic.data.Record;
import org.apache.wayang.basic.types.RecordType;
import org.apache.wayang.core.function.FunctionDescriptor;
import org.apache.wayang.core.function.TransformationDescriptor;
import org.apache.wayang.core.types.BasicDataUnitType;

/**
 * This descriptor pertains to projections. It takes field names of the input
 * type to describe the projection.
 */
public class ProjectionDescriptor<Input, Output> extends TransformationDescriptor<Input, Output> {

    /**
     * Java implementation of a projection on POJOs via reflection.
     */
    // TODO: Revise implementation to support multiple field projection, by names
    // and indexes.
    private static class PojoImplementation<Input, Output>
            implements FunctionDescriptor.SerializableFunction<Input, Output> {

        private final String fieldName;

        private Field field;

        private PojoImplementation(final String fieldName) {
            this.fieldName = fieldName;
        }

        @Override
        @SuppressWarnings("unchecked")
        public Output apply(final Input input) {
            // Initialization code.
            if (this.field == null) {

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