Unable to use @include or @skip when stitching

[tunurgitr]

Describe the bug
Stitched queries that use @include or @skip directives that refer to a variable return a message that the variable is not declared. This effectively means that @include and @Skip don't work when stitching as the primary use-case would be having them handle a variable.

To Reproduce
Steps to reproduce the behavior:

1. Create a stitched schema
2. Attempt to use an @include directive with a boolean field in playground. For example:

query TEST($ok:Boolean!) {
  hey {
    hello @include(if:$ok)
  }
}

3. Note the error: "The following variables were not declared: YOUR_VARIABLE."

Expected behavior
Same behavior as if the literal true or false were passed to the @include directive.

Additional context
In some limited debugging, it looks like these variables are not in the _usedVariables list in AllVariablesUsedVisitor.cs, I'm guessing they're not being sent to the client endpoint, but I haven't dug-in that deep.

[michaelstaib]

OK, this one is more complicated :) the query rewriter does not correctly visit the directive hence the variables are not touched. I will look at this tomorrow.

[michaelstaib]

This bug is now fixed.