Update queries for latest 2.3 schema and add validator script

[zetlen]

This PR is a:

[ ] New feature
[ ] Enhancement/Optimization
[ ] Refactor
[x] Bugfix
[ ] Test for existing code
[ ] Documentation

Summary

As of magento/graphql-ce#132 the Product schema has changed; the small_image is now an object with url and path parameters. This PR updates the corresponding queries, prop types, and tests to handle this change.

When merged, this will make Venia incompatible with Magento 2.3 prior to this commit.

For developer discoverability, this PR adds a script which validates queries against the connected Magento instance: npm run-script validate:venia:gql.

Error example:

In a later PR, it would be a good idea to run this validator every time a query changes, or when a Magento instance is connected...

[zetlen]

Because this validation is dependent on a connected Magento instance, I haven't integrated it into the test suite or CI. Right now, we don't have a connected Magento instance for either.

[PWAStudioBot]

Fails

🚫

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Generated by 🚫 dangerJS

[coveralls]

Pull Request Test Coverage Report for Build 1099

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 20.376%

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Totals
Change from base Build 1097:	0.04%
Covered Lines:	387
Relevant Lines:	1977

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💛 - Coveralls

[jimbo]

Seems to work as advertised. This will be a helpful addition. 👍

Just two minor changes requested.

[pcvonz]

Works fine on my end!