fix(plugin-chart-table): preserve comparison arrow when a column-specific formatter entry is missing

The per-cell comparison arrow and arrow color are computed twice: once
from the row-level basicColorFormatters, then unconditionally reassigned
from basicColorColumnFormatters when that array is present. Unlike the
sibling backgroundColor assignment (which falls back to the prior value
via `|| backgroundColor`), the arrow and arrowColor reassignments had no
such fallback, so a row missing an entry in basicColorColumnFormatters
lost its arrow entirely and would have flipped its arrow color, even
though a valid value had already been computed from basicColorFormatters.

Falls back to the previously-computed value in both cases, same as
backgroundColor already does.

superset-frontend/plugins/plugin-chart-table/src/TableChart.tsx

@@ -1138,7 +1138,8 @@ export default function TableChart<D extends DataRecord = DataRecord>(
                 ?.backgroundColor || backgroundColor;
             arrow =
               column.label === comparisonLabels[0]
-                ? basicColorColumnFormatters[row.index]?.[column.key]?.mainArrow
+                ? (basicColorColumnFormatters[row.index]?.[column.key]
+                    ?.mainArrow ?? arrow)
                 : '';
           }
           const rowSurfaceColor =
@@ -1209,15 +1210,18 @@ export default function TableChart<D extends DataRecord = DataRecord>(
             basicColorColumnFormatters &&
             basicColorColumnFormatters?.length > 0
           ) {
-            arrowStyles = css`
-              color: ${
-                basicColorColumnFormatters[row.index]?.[column.key]
-                  ?.arrowColor === ColorSchemeEnum.Green
-                  ? theme.colorSuccess
-                  : theme.colorError
-              };
-              margin-right: ${theme.sizeUnit}px;
-            `;
+            const columnArrowColor =
+              basicColorColumnFormatters[row.index]?.[column.key]?.arrowColor;
+            if (columnArrowColor) {
+              arrowStyles = css`
+                color: ${
+                  columnArrowColor === ColorSchemeEnum.Green
+                    ? theme.colorSuccess
+                    : theme.colorError
+                };
+                margin-right: ${theme.sizeUnit}px;
+              `;
+            }
           }
 
           const cellProps = {

superset-frontend/plugins/plugin-chart-table/test/TableChart.test.tsx

@@ -2125,8 +2125,18 @@ describe('plugin-chart-table', () => {
           'rgba(0, 150, 0, 0.2)',
         );
 
-        // the row missing a formatter entry still renders its raw value
-        expect(screen.getAllByTitle('110').length).toBeGreaterThan(0);
+        // the row missing a formatter entry falls back to the row-level
+        // comparison arrow instead of losing it: before the fix, this row's
+        // arrow was silently cleared (and its color, computed the same way,
+        // would have flipped to the "decrease" color) whenever the
+        // column-specific lookup for this row was undefined.
+        const arrowCell = screen
+          .getAllByTitle('110')
+          .find(cell => cell.querySelector('span'));
+        expect(arrowCell).toHaveTextContent('↑110');
+        expect(getComputedStyle(arrowCell!).background).toContain(
+          'rgba(0, 150, 0, 0.2)',
+        );
       });
 
       test('preserves client-side search text across temporal table rerenders', async () => {