feat(Datagrid): add support for dynamic sub rows

[matthewgallo]

Closes #5600

This PR adds support for dynamic sub rows/nested rows. To use this functionality, provide getAsyncSubRows to the useDatagrid hook and resolve a promise upon receiving/fetching sub rows and updating your data.

const datagridState = useDatagrid(
    {
      columns,
      data,
      getAsyncSubRows: async (row) => {
        // ONLY update/simulate fetch of new sub rows
        // if the current row doesn't already have any
        if (row.subRows.length) return;
        await new Promise((resolve) => {
          setTimeout(() => {
            // For the sake of this example, we will show
            // a skeleton for subRows fetching dynamic subRows
            // but won't update data with anything
            if (row.depth > 0) {
              return resolve();
            }
            const newRows = makeData(2, { id: 'test-id' });
            const clonedData = [...data];
            const rowIndexToUpdate = clonedData.findIndex(
              (r) => r.id === row.original.id
            );
            clonedData[rowIndexToUpdate].subRows = newRows;
            setData(clonedData);
            resolve();
          }, 1000);
        });
      },
    },
    useNestedRows
  );

What did you change?

packages/ibm-products-styles/src/components/Datagrid/styles/_useNestedRows.scss
packages/ibm-products/src/components/Datagrid/Datagrid/DatagridRow.tsx
packages/ibm-products/src/components/Datagrid/Datagrid/addons/stateReducer.js
packages/ibm-products/src/components/Datagrid/Extensions/NestedRows/NestedRows.stories.jsx
packages/ibm-products/src/components/Datagrid/types/index.ts
packages/ibm-products/src/components/Datagrid/useNestedRowExpander.js
packages/ibm-products/src/components/Datagrid/useRowRenderer.js
packages/ibm-products/src/components/Datagrid/utils/makeData.js

How did you test and verify your work?

Storybook

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[devadula-nandan]

LGTM