Table row grouping

[atmgrifter00]

Pull Request

🤨 Rationale

• Programmatic grouping of data rows #1003

👩‍💻 Implementation

Following the mixin pattern for fractional width columns, I have created a mixin for allowing columns to opt in to being groupable.

To render the group row, I have created a TableGroupRow component, which encapsulates the expand/collapse button as well as the rendered visual representing the grouped value, as well as the count of the number of rows "parented" under the group row.

This PR does not include:

• Angular/Blazor integration
• Keyboard navigation
• Updated row stylings for hover states
• Styling/layout changes related to the presence of a "collapse-all" button in the header (which will be added later).

🧪 Testing

Unit tests.

✅ Checklist

• I have updated the project documentation to reflect my changes or determined no changes are needed.

[jattasNI]

Initial feedback on the story and component behavior; haven't looked at the code yet.

[jattasNI]

Just some quick initial feedback post-refactor from playing with the storybook. Will review the new code tomorrow (possibly after you've addressed Molly's feedback).