restoreCartItem mutation

[kidunot89]

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What does this implement/fix? Explain your changes.

Adds restoreCartItem mutation

mutation restoreCartItem( $input: RestoreCartItemInput! ) {
    restoreCartItem( input: $input ) {
        clientMutationId
        cartItem {
            key
            product {
                id
            }
            variation {
                id
            }
            quantity
            subtotal
            subtotalTax
            total
            tax
        }
    }
}

RestoreCartItemInput definition

'clientMutationId' => array(
	'type'        => array( 'non_null' => 'ID' ),
	'description' => __( 'Unique ID for mutation', 'wp-graphql-woocommerce' ),
),
'key' => array(
	'type'        => array( 'non_null' => 'ID' ),
	'description' => __( 'Cart item key of the item being removed', 'wp-graphql-woocommerce' ),
),

Does this close any currently open issues?

…

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

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Any other comments?

…

Where has this been tested?

Operating System: Ubuntu 18.04

WordPress Version: 5.2