Use shorter imports for Component, TestGroup, etc.

[xylar]

This is more consistent with the API documentation, which uses the shorter names, and also what we want folks to use in new test groups they make.

Checklist

• [x] Developer's Guide has been updated
• [x] Documentation has been built locally and changes look as expected
• [x] Testing comment in the PR documents testing used to verify the changes

[xylar]

Testing

I tested this by successfully running several baroclinic channel and cosine bell tests on Chrysalis (comparing with a baseline).

[xylar]

This is something that has been bugging me while I write the tutorial.