Fixed Table flex column layout error #30437 (#30470)

RenderTable._computeColumnWidths() had a logic error that caused flex columns to be collapsed to their minimum widths in certain situations dependent on the layout width constraint and the number of flex columns.

packages/flutter/lib/src/rendering/table.dart

@@ -958,8 +958,8 @@ class RenderTable extends RenderBox {
                 deficit -= widths[x] - minWidths[x];
                 widths[x] = minWidths[x];
               } else {
-                deficit -= availableDelta;
-                widths[x] -= availableDelta;
+                deficit -= delta;
+                widths[x] -= delta;
                 newAvailableColumns += 1;
               }
             }

packages/flutter/test/rendering/table_test.dart

@@ -47,6 +47,19 @@ void main() {
     expect(table.size, equals(const Size(0.0, 0.0)));
   });
 
+  test('Table control test: constrained flex columns', () {
+    final RenderTable table = RenderTable(textDirection: TextDirection.ltr);
+    final List<RenderBox> children = List<RenderBox>.generate(6, (_) => RenderPositionedBox());
+
+    table.setFlatChildren(6, children);
+    layout(table, constraints: const BoxConstraints.tightFor(width: 100.0));
+
+    const double expectedWidth = 100.0 / 6;
+    for (RenderBox child in children) {
+      expect(child.size.width, moreOrLessEquals(expectedWidth));
+    }
+  });
+
   test('Table test: combinations', () {
     RenderTable table;
     layout(RenderPositionedBox(child: table = RenderTable(