Allow field visibility transformation to remove interface relationships - #4419

Summary

• add a dedicated predicate and environment for controlling individual interface implementation relationships
• apply field and relationship visibility in the same schema transformation so related removals are validated atomically
• preserve existing constructor behavior by retaining all interface relationships unless the new predicate is supplied
• retain the existing reachability cleanup and fail schema construction for invalid transitive interface removals
• mark graphql.schema.transform as @NullMarked and enforce package-level JSpecify annotations in the architecture test

Testing

• ./gradlew test --tests graphql.schema.transform.FieldVisibilitySchemaTransformationInterfaceImplementationTest
• ./gradlew test --tests graphql.schema.transform.FieldVisibilitySchemaTransformationTest
• ./gradlew test --tests graphql.archunit.JSpecifyAnnotationsCheck --tests graphql.schema.transform.FieldVisibilitySchemaTransformationInterfaceImplementationTest --tests graphql.schema.transform.FieldVisibilitySchemaTransformationTest (63 tests)
• ./gradlew test (5,700 tests)
• ./gradlew jacocoTestReport
• ./gradlew javadoc --info --stacktrace

The changed transformer and relationship-removal visitor have 100% line, branch, and method coverage.