fix(hydration): ignore host scope token in class validation

[nolanlawson]

Details

Fixes #4853

This is only a partial solution to the problem – I have a follow-up for further edge cases: #4866

With this PR, when we render the host scope token (e.g. class="lwc-abc123-host"), we also encode it as a data-lwc-host-scope-token attribute. This tells hydration to ignore certain classes during class validation, which avoids timing issues when using scoped styles and render().

To solve this, I'm also simplifying our class validation logic to only look at the differences between two Set<string>s. I just don't think it's worth it to care about classes in different orders, or duplicate classes – this doesn't affect CSS styling, and it makes the logic much simpler.

Does this pull request introduce a breaking change?

• 😮‍💨 No, it does not introduce a breaking change.

Does this pull request introduce an observable change?

• 🤞 No, it does not introduce an observable change.