Product to ProductInterface

[kidunot89]

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What does this implement/fix? Explain your changes.

TODO

• Update summary to match the official changes to come.

Replace Product with ProductUnion

New object types

• SimpleProduct
• VariableProduct
• ExternalProduct
• GroupProduct

New union types

• ProductUnion

Removed types

• Product

query {
  product(id: "") {
    ... on VariableProduct {
      id
      name
      variations {
        nodes {
          id
          name
        }
      }
    }
  }
  productBy(productId: 1000) {
    ... on SimpleProduct {
      id
      name
    }
  }
  products {
    nodes {
      ... on SimpleProduct {
        id
        name
        salePrice
        regularPrice
        price
      }
      ... on ExternalProduct {
        id
        name
        buttonText
        externalUrl
      }
      ... on GroupProduct {
        id
        name
        addToCartText
        addToCartDescription
        products {
          nodes {
            ... on SimpleProduct {
              id
              name
              salePrice
              regularPrice
              price
            }
          }
        }
      }
    }
  }
}

Does this close any currently open issues?

…

Any relevant logs, error output, GraphiQL screenshots, etc?

(If it’s long, please paste to https://ghostbin.com/ and insert the link here.)

Any other comments?

…

Where has this been tested?

Operating System: Linux Mint 19.2

WordPress Version: 5.2.3