Relax prop validation on getSelectedProductOptions and getSelectedProductOptions

[blittle]

WHY are these changes introduced?

The getPaginationVariables and getSelectedProductOptions utility functions validate that an argument is always an instanceof Request. While helpful, it also can be a pain when passing an object that looks exactly the same as a Request but isn't an instance of the class.

WHAT is this pull request doing?

Still validate, but instead just test if the the object contains the url property.

HOW to test your changes?

Post-merge steps

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes
• I've added tests to cover my changes
• I've added or updated the documentation