Improve cell focus behavior

[seancolsen]

Fixes #1892
Fixes #2380

Notes

• I started working on Re-focus table cell after opening record selector on that cell #1892 first but ended up chasing down Synchronize cell "active" and "focused" states #2380 in the process. That's why this PR addresses them both.
• Re-focus table cell after opening record selector on that cell #1892 is pretty straightforward, and I think it should be easy to see that this PR addresses it. Launch the record selector from an FK cell. Close the selector either by submitting a value or by closing the model. Before this PR, the FK cell would no longer be focused (although it was hard to tell). After this PR, the cell regains focus, allowing you to use the keyboard to continue navigating from cell to cell.
• Synchronize cell "active" and "focused" states #2380 is the more nebulous issue, where we had some discussion in the ticket about various implementation approaches and only seemed to reach a clear agreement on the main objective. So this PR is a rough stab at addressing that main objective. Basically: the cell still has an 'active' state, kept separate from its focused state; but now the cell is styled differently depending on whether it is focused. We had previously styled the cell outline gray for disabled cells. I repurposed that gray styling to indicate the state when the cell is active but no focused.
• I agree with @pavish that we need to retain state to track when a cell is active but not focused. And I think we're both in agreement that we should try to prevent the user from inadvertently causing the cell to enter this state. For example, after the record selector closes, we should re-focus the cell to avoid the "active but not focused" state.
• What's nice about these changes is it makes it easier for us devs to spot that pesky "active but not focused" state. In playing with the app after these changes, I noticed and reported two new bugs: Cell loses focus when clicking on its outline #2987 URL cell loses focus when clicking on its contained hyperlink #2988

Before

• Cell outline was blue when cell was active and not disabled.
• Cell outline was gray when cell was active and disabled.
• The focus state did not affect the cell outline.
• Opening and closing the record selector caused the cell to lose focus

After

• Cell outline is blue when the cell is active and focused.
• Cell outline is gray when the cell is active and not focused.
• Cell has no outline otherwise
• The cell is re-focused after the record selector closes

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
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• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.

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[pavish]

Looks great! Nice work!