`_id` Omitted from Customized Fields

[tubbo]

Describe the bug
Any customized fields ending in _id will have the _id omitted from their instance variable name, which causes issues if that name conflicts with an ivar or method that already exists.

To Reproduce
Steps to reproduce the behavior:

1. Add a customized field called :product_id
2. Create your customizations with MyCustomizations.new('1234', 'product_id' => '5678')
3. Call customizations.product_id, it will be "1234".

Expected behavior
Since the product_id param overrides the @product_id assigned by the first argument, the value of #product_id in the customization object should be "5678". Digging in reveals that the value of "5678" was actually assigned to @product, not @product_id.

Workarea Setup (please complete the following information):
Workarea v3.4

Additional context
This was originally reported by John Varady on discourse.