Fix prototype-colliding names in execution values

[abishekgiri]

Summary

Fixes an issue where prototype-colliding property names (e.g., __proto__, constructor) could interfere with execution value handling.

Changes

• Ensured own-property checks are used when accessing execution values
• Prevent potential prototype chain collisions

Motivation

JavaScript objects can inherit properties from the prototype chain. Without proper checks, this can lead to unexpected behavior when handling execution values.

Testing

• Verified manually with edge-case inputs involving prototype properties
• Existing tests pass locally

[vercel]

@abishekgiri is attempting to deploy a commit to the The GraphQL Foundation Team on Vercel.

A member of the Team first needs to authorize it.

[abishekgiri]

Status update

• Fixed execution/values.ts so getArgumentValues() and getVariableValues() keep their null-prototype maps instead of reintroducing Object.prototype via object spread.
• Added regression coverage for omitted prototype-colliding names like toString in both resolver args and coerced variable values.
• Results: targeted mocha, eslint, and prettier checks passed for this change.
• tsc in this environment still reports existing external errors from ../node_modules/@types/react-dom, which are outside this PR.