@link should report an error on unknown directives

[martinbonnin]

Description

extend schema @link(
  url: "https://specs.apollo.dev/nullability/v0.4", 
  # Unknown directive are allowed here
  import: ["@semanticNonNull", "@foobar"]
)

[martinbonnin]

Fixed in #6164. This now fails with:

> A failure occurred while executing com.apollographql.apollo.gradle.internal.GenerateSources
   > e: /Users/martinbonnin/Downloads/test-stuff/src/main/graphql/schema.graphqls: (5, 15): Apollo: unknown definition '@foobar'
     ----------------------------------------------------
     [4]:
     [5]:extend schema @link(
     [6]:    url: "https://specs.apollo.dev/nullability/v0.4",
     ----------------------------------------------------

[github-actions]

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