Add tests of DlData

[matthew-white]

This PR adds tests of the new DlData component. That component was added in #1074, but tests weren't updated as part of that PR. DlData is tested indirectly through the tests of EntityData. However, I think it'd be better to add tests of DlData specifically, then just test that EntityData passes the correct props to DlData. The entity hover card will use DlData, and I'll want to test it in a similar way, testing that it passes the correct props.

The existing tests of EntityData were already pretty comprehensive, so I'm basically just moving them and reworking them to mount DlData instead of EntityData.

Before submitting this PR, please make sure you have:

• run npm run test and npm run lint and confirmed all checks still pass OR confirm CircleCI build passes
• verified that any code or assets from external sources are properly credited in comments or that everything is internally sourced