feat(Tile): update Tile AI styles to phase 3 spec

[tw15egan]

Closes #15946

Updates AI Tile to phase 3 spec

Changelog

Changed

• Adjusted a few drop shadows, removed underline when clickable tile is focused / hovered

Testing / Reviewing

Ensure Tile matches AI phase 3 spec

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[tay1orjones]

LGTM

[aagonzales]

The gradient is bleeding to high in the tile, I can't tell where the problem is coming from though.

[tw15egan]

@aagonzales, we added the 15% stop for the hover gradient mixin; perhaps we need to add it to the base one as well? Just be aware that this is the same gradient background as the callout (Tile just uses $layer as the background), so it would also affect that gradient.

[aagonzales]

@tw15egan ok, can you add it and I'll check both to make sure it still looks ok.

[tw15egan]

@aagonzales updated. If that doesn't work, we can always break the Tile into it's own gradient like we did with DataTable

[aagonzales]

I think that did it, it looks right to me now. Work fine for callout too.