GraphQLExecutionSource/DataDict/ObjectData Refactor

[AnthonyMDev]

This PR:

• Defines a new GraphQLExecutionSource that is passed to GraphQLExecutor.
  • The execution source determines how fields in the data are read, what the underlying type for nested entity fields in the data is stored as, how to compute which selections and fulfilled fragments should be executed, and how to expose the source data for cache key resolution.
  • These were all being determined by different closures passed to the executor and some tightly coupled implementation details inside of the executor. Now they are grouped sensibly into accurate sets of configuration for the defined execution sources.
  • Defines execution sources for Network Response Data; Cache Response Data, and Selection Set Models.
  • By making the executor generic over it's source, we get generic specialization and additional type safety that improves both the code quality and performance of GraphQLExecutor.
• Defines an ObjectData protocol to use for wrapping the data from individual execution sources while completing cache key resolution.
  • Because the shape and underlying types of raw data for each source differs, cache key resolution is inconsistent.
  • Implementations of ObjectData provide an opaque wrapper that lazily accesses and transforms the data for each execution source.
    • This should provide a consistent API for accessing data while computing cache keys.
    • This PR defines the data transformers for each of the necessary execution sources.
    • Breaking Change: The API for cache key resolution in SchemaConfiguration will be changing to use the new ObjectData protocol. This is a very minor breaking change for most users during the next version upgrade. Detailed explanation and documentation will be included to minimize confusion and impact to users during the upgrade.
    • This PR includes the initial changes to code generation templates to generate selection set initializers with the new DataDict shape. Additional work and unit tests to ensure code generation addresses all edge cases will come in following PRs on this stack.
• DataDict refactoring:
  • Separates the fulfilledFragments from the object data in DataDict.
  • This allows us to operate on the fulfilledFragments (and any other future metadata on SelectionSets) without polluting the object's data dictionary.
  • Equatable and Hashable conformance for DataDict only check the data, not the fulfilledFragments. This fixes Equality operator shows incorrect values based on value of "__fulfilled" #2944.
  • DataDict now uses a class for storage with copy-on-write value semantics.
    • Early performance testing shows a 10-20% improvement in parsing and execution performance and a 65-75% improvement in type case conversion accessors and manual selection set model initialization!

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[AnthonyMDev]

Invert this paragraph for clarity

[AnthonyMDev]

Maybe make this conform to sequence for iterations?