Allow @external partial references without redefining entire type

[smyrick]

Today if I need to reference a type because I am using something like @requires, I need to mark the type and field as @external. However if this type also has more fields which I don't reference in my @requires and I do not include them in my separate definition, I get the Federation hint INCONSISTENT_OBJECT_VALUE_TYPE_FIELD.

For example

Subgraph One

extend schema
    @link(
        url: "https://specs.apollo.dev/federation/v2.5",
        import: ["@key", "@requires", "@external", "@shareable"]
    )

type Query {
  locations: [Locations]
}

type Location @key(fields: "id"){
    id: ID!
    name: String!
    description: String!
    foo: Foo
}

type Foo {
    a: String
    b: String
    c: String
}

Subgraph Two

extend schema
    @link(
        url: "https://specs.apollo.dev/federation/v2.5",
        import: ["@key", "@requires", "@external", "@shareable", "@inaccessible"]
    )

type Location @key(fields: "id") {
    id: ID!
    overallRating: Float @requires(fields: "foo { a }")
    foo: Foo @external
}

type Foo {
    a: String @external
}

This composes without errors but I do get a HINT

HINT: [INCONSISTENT_OBJECT_VALUE_TYPE_FIELD]: Field "Foo.b" of non-entity object type "Foo" is defined in some but not all subgraphs that define "Foo": "Foo.b" is defined in subgraph "locations" but not in subgraph "reviews".
HINT: [INCONSISTENT_OBJECT_VALUE_TYPE_FIELD]: Field "Foo.c" of non-entity object type "Foo" is defined in some but not all subgraphs that define "Foo": "Foo.c" is defined in subgraph "locations" but not in subgraph "reviews".

What I would like

In subgraph two (reviews), it would be nice to not have to redefine the entire Foo type when I am only using it for @external references and I only need to reference Foo.a.

If I now update the Foo type to include a new field Foo.d, I have to go to many locations to do that when it is not even used there