[apollo-ast] Add GQLDocument.validate(SchemaValidationOptions) to allow adding external schemas.

[martinbonnin]

Also add support for kotlin_labs/v0.4

val cacheControlSchema = ForeignSchema("cache", "v0.1", definitions)

schemaString.toGQLDocument().validateAsSchema(
    SchemaValidationOptions(
        addKotlinLabsDefinitions = false,
        foreignSchemas = listOf(cacheControlSchema)
    )
).getOrThrow()

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[BoD]

🚀

[BoD]

Hey actually, maybe this should be allowed? In my case, the cache gradle plugin can add the cache foreign definitions 👍 - but users will still also apply the regular apollo gradle plugin, which won't accept the extend schema @link(url: "https://specs.apollo.dev/cache/v0.1" import: ...) with this check.

[martinbonnin]

Yikes. Good point. I still think this is something we want to validate. For an example, someone asking for nullability/v0.1 support should get an error: this is not supported anymore.
Yet another argument for a plugin API. Schema validation should be done only once. But plugins could contribute foreign schemas. I'll open a separate PR

[martinbonnin]

Follow up PR #6165