fix: allow restrictions on nested properties

[range123]

Resolves #6501
Impact: minor
Type: bugfix

Issue

The checks for shipping restrictions based on an item's properties only work top for level properties in the item. It doesn't work for nested properties such as price.amount or subtotal.amount.

Steps to reproduce:

1. Create a product, create a variant with the price attribute set.
2. Create a shipping method.
3. Create a "deny" shipping restriction with the attribute price.amount which would exclude the shipping method for the product if it was applied.
4. See that the shipping method is available for the cart in checkout process even when it shouldn't be (based on restriction price value).

Solution

Can be solved by using lodash _.get() for getting the nested property from the item, instead of using the default javascript getter. This would make sure the restrictions work with both nested and non-nested attributes.

Testing

1. Create a product, create a variant with the weight and price attribute set.
2. Create a shipping method.
3. Create "deny" shipping restriction with the attribute weight which would exclude the shipping method for the product if it was applied.
4. Create another "deny" shipping restriction with the attribute price.amount which would exclude the shipping method for the product if it was applied.
5. See that the shipping method is available/unavailable for the cart in checkout process (based on the restrictions).

[changeset-bot]

🦋 Changeset detected

Latest commit: 769c218

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@reactioncommerce/api-plugin-shipments-flat-rate	Patch

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[brent-hoover]

@range123 I would like to see a test case for this

[range123]

Added tests! @zenweasel