Support graphql oneOf directive without composeDirective

[jdolle]

Apollo doesn't support oneOf because they are using an out dated version of graphql.

This PR adds functionality to keep the oneOf directives through composition and adds a test to ensure this works.

This avoids having to unnecessarily add @composeDirective for @oneOf. @composeDirective should be reserved for custom directives instead of native directives.

[gemini-code-assist]

Code Review

This pull request adds support for composing the built-in @oneOf directive on input object types during supergraph composition. It updates the subgraph state builder to parse @oneOf on input objects, propagates this state through the supergraph composition AST, and outputs the directive in the resulting supergraph and public SDLs. Additionally, a skipApolloBuildCheck option was added to the test kit to bypass Apollo Gateway validation when needed. Feedback on the changes highlights two issues: a leftover test.only modifier in the new test file that would cause other tests to be skipped, and a leftover console.log debugging statement in validate-state.ts.

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[jdolle]

only run for guild b/c others dont support atm

[jdolle]

must ensure the definition is added or else Supergraph.build fails because the internal version of graphql it's using is out of date

[kamilkisiela]

Few things:

• What will happen if subgraph A already has @oneOf defined via @composeDirective, and after we introduce native support for it, subgraph B adds @oneOf without @composeDirective
• Let's add a few scenarios where you try to "break" it, like two subgraphs defining the same input type, a case where the input type is defined twice in two subgraphs, but fields differ, where one defines @oneOf and the other does not etc