Add transforms to wrap, extract, and rename fields

[yaacovCR]

Original post edited to reflect changes in graphql-tools-fork v6.3.2 that support error mapping.

This is now live in graphql-tools-fork v6.3.2.

Examples are within the tests.

For instance, the following extracts fields from an enclosing type in the original schema:

    transformedPropertySchema = transformSchema(propertySchema, [
      new ExtendSchema({
        typeDefs: `
          extend type Property {
            locationName: String
          }
        `,
        resolvers: {
          Property: {
            locationName: createMergedResolver({ fromPath: ['location', 'name'] }),
          },
        },
        fieldNodeTransformerMap: {
          'Property': {
            'locationName':
              fieldNode => wrapFieldNode(renameFieldNode(fieldNode, 'name'), ['location']),
          },
        },
      }),
    ]);

The following wraps fields in multiple new layers:

    transformedPropertySchema = transformSchema(propertySchema, [
      new ExtendSchema({
        typeDefs: `
          extend type Property {
            outerWrap: OuterWrap
          }
          type OuterWrap {
            innerWrap: InnerWrap
          }
          type InnerWrap {
            id: ID
            name: String
          }
        `,
        resolvers: {
          Property: {
            outerWrap: (parent, args, context, info) => ({
              innerWrap: {
                id: createMergedResolver({ toPath: ['innerWrap', 'id'] })(parent, args, context, info),
                name: createMergedResolver({ toPath: ['innerWrap', 'name'] })(parent, args, context, info),
              },
            }),
          },
        },
        fieldNodeTransformerMap: {
          'Property': {
            'outerWrap': (fieldNode, fragments) => extractFields({ fieldNode, path: ['innerWrap'], fragments }),
          },
        },
      }),

Feedback is welcome!