Backport 26.1: validate circular default values - #4450

Backport of #4253 to the 26.x maintenance branch.

Input object fields can define default values in ways that form cycles. For example:

input A { b: B = {} }
input B { a: A = {} }

The defaults form an infinitely expanding value. This PR implements the specification InputObjectDefaultValueHasCycle validation so these schemas are rejected during schema validation instead of overflowing while defaults are coerced.

Implementation notes:

• Uses one shared traversal for literal and programmatic defaults.
• Supports the same programmatic list representations as GraphQL Java coercion, including Java arrays.
• Detects cycles before external argument and field defaults are coerced.
• Creates fresh validation-rule instances for each schema-validation run.
• Consolidates the SDL cases into data-driven tests and removes the duplicate integration test class.

This behavior matches the GraphQL specification and graphql-js v17 implementation:

• https://spec.graphql.org/draft/#InputObjectDefaultValueHasCycle()
• RFC: Default value validation & coercion graphql/graphql-js#3814