fix: including Lit table styles in the dom-module

[dlockhart]

I missed one use case: using <d2l-table-wrapper> from inside a Polymer element. In that scenario, the styles were getting added to the root document but couldn't pierce the wrapper element's shadow root so weren't getting applied.

This change just moves them into the style dom-module just like the older d2l-table/d2l-tr/etc. styles.

The unfortunate side-effect of all this is that Polymer elements will need to continue to use the Polymer version of d2l-table, and Lit ones will need to use the Lit version -- no mixing and matching. So that kind of goes against how web components work... but I'm justifying it in my mind by thinking of these more as shared styles than a web component. In Polymer the way you share styles is these dom-modules and in Lit it's importing style literals into your component. 🤷

[ghost]

🎉 This PR is included in version 2.8.1 🎉

The release is available on GitHub release

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