New Generic Field Rewriter & Custom Rewriter

[AndresPrez]

@chanind Ive added a new Rewriter: FieldRewriter inspired by the ScalarFieldToObjectFieldRewriter and a CustomRewriter to allow custom implementation of the Rewriter public methods.

PR should be backwards compatible and comes with unit tests.

New functionalities:

• Scalar to object with renaming: Similar to ScalarFieldToObjectFieldRewriter, but it can also rename the field in question.
• Pass in field arguments from variables: In addition to converting a scalar field to an object field, it implements the ability to pass arguments to such field.
• Support for aliases: Understands aliases in incoming queries, and can also rename fields with aliasing.
• Adds nodeAndParent context variable to rewriteResponse fn: Useful for response rewrites that need to know what the query was initially (e.g, for __typename response rewrites).

[chanind]

Apologies for the delay getting this reviewed, I'm traveling this week so it might take a few more days before I can get this reviewed and merged. I'll aim to do so by early next week at the latest. Thank you so much for submitting this! It looks like a great improvement.