[GraphQL] Support @skip and @include directives

https://spec.graphql.org/October2021/#sec-Type-System.Directives

skip

directive @skip(if: Boolean!) on FIELD | FRAGMENT_SPREAD | INLINE_FRAGMENT

The @skip built-in directive may be provided for fields, fragment spreads,
and inline fragments, and allows for conditional exclusion during execution as
described by the if argument.

In this example experimentalField will only be queried if the variable
$someTest has the value false.

query myQuery($someTest: Boolean!) {
  experimentalField @skip(if: $someTest)
}

include

directive @include(if: Boolean!) on FIELD | FRAGMENT_SPREAD | INLINE_FRAGMENT

The @include built-in directive may be provided for fields, fragment
spreads, and inline fragments, and allows for conditional inclusion during
execution as described by the if argument.

In this example experimentalField will only be queried if the variable
$someTest has the value true

query myQuery($someTest: Boolean!) {
  experimentalField @include(if: $someTest)
}

Note: Neither @skip nor @include has precedence over the other. In the case
that both the @skip and @include directives are provided on the same
field or fragment, it must be queried only if the @skip condition is false
and the @include condition is true. Stated conversely, the field or fragment
must not be queried if either the @skip condition is true or the
@include condition is false.

Start with the linked October 2021 GraphQL specification sections for the built-in @skip and @include directives. Trace the repository's GraphQL directive validation and execution entry points, then verify that fields, fragment spreads, and inline fragments follow both conditions and the stated combined behavior.