Improve input validation with visitor

[lopert]

Part of https://github.com/shop/issues-shopifyvm/issues/660

Leverages graphql's visit to traverse the inputQueryAST

[adampetro]

Let's squash these commits down either before merging or by using squash-and-merge

[saga-dasgupta]

Sorry late comment but didn't we convert all the fragment spreads in the first step? why do we need this in this condition?

[lopert]

I think you're right that this could be removed, since everything should have converted to inline fragments during this call

shopify-function-test-helpers/src/methods/validate-fixture-input.ts

Line 37 in 32b548a

const inlineFragmentSpreadsAst = inlineNamedFragmentSpreads(queryAST);