feat: create @requires integration that functions like a normal resolver

The explicit_requires flag currently generates the @requires resolver inside the execution context. It also doesn't use the normal resolver resolution process and adds a custom implementation that is always called, even if the field isn't requested.

The new computed_requires flag looks for @requires directives and mutates the schema to add dynamic field arguments and directives that are used internally by gqlgen.

These additional directives (@entityReference and @populateFromRepresentations) are runtime directives that "computed_requires" adds implementations for that enable us to fetch the correct data from the representations array and populated it into the dynamic argument for the @requires field.

The new implementation still isn't typesafe and generates the required fields into a map[string]any. This is the same as the existing explicit_requires implementation.

We will follow up with type safety in a future PR. To support type safety we need to generate types and marshaling logic for GraphQL operations (vs just schemas like we do today) which is a large lift.

I have:

[x] Added tests covering the bug / feature (see testing)
[x] Updated any relevant documentation (see docs)

99designs / gqlgen

feat: create @requires integration that functions like a normal resolver #3292