fix: Fix modal causing body padding to increase when unmounted

[suzubara]

Summary

I fixed this issue by consolidating some of the code that handles DOM changes when the modal is opened & closed, and explicitly resetting body padding when its closed instead of toggling between the two values.

I also added to the docs about how to use yarn link to test the library locally with a NextJS app.

Related Issues or PRs

Fixes #1898

How To Test

• You can test this on an application that uses the Modal component by causing the modal to mount & unmount (typically by navigating to a new page). Without this fix, the padding-right on the body element would continue to increase by 15px (or the width of your scrollbar)
• Tested & verified on Space Force
• I also added a test case for this that was failing without the fix.

[github-actions]

	Warnings
⚠️	This PR does not include changes to storybook, even though it affects component code.

Generated by 🚫 dangerJS against 7d727fe

[brandonlenz]

Nice! I did some smoke testing in deployed storybook, but I trust your local testing with your project code (plus the test coverage here for the issue is great!)

Also glad to see what looks like prettier catching some formatting quirks that snuck through 🥳

The handleOpen/CloseEffect make things nice and clear too 🎉