Fix/shadowrootmode

[spmonahan]

Pull Request

📖 Description

Changes the shadowroot attribute on <template>s to shadowrootmode per the standardized declarative shadow DOM when server rendering components.

👩‍💻 Reviewer Notes

web.dev notes that pre-standardization, Chrome and Edge used the shadowroot attribute instead. This attribute doesn't work in any current version of the browsers I tested in so I've removed it entirely. This seems a reasonable choice to me since this package is still in beta and the versions of Chrome and Edge that support the non-standard attribute are quite old at this point, however, if it's necessary to support the non-standard attribute I'm happy to do that work but I will need guidance on how to test against older browser versions.

📑 Test Plan

I updated relevant tests in the repo and validated the before and after in Edge, Chrome, Safari and Firefox.

This is my test repo.

Before

Edge

Chrome

Firefox

Safari

After

Edge

Chrome

Firefox

Safari

✅ Checklist

General

• [x] I have included a change request file using $ yarn change
• [x] I have added tests for my changes.
• [x] I have tested my changes.
• [X] I have read the CONTRIBUTING documentation and followed the standards for this project.