feat(demo): add demo for HeightByRowsHelper

Close FlowingCode#98

src/test/java/com/flowingcode/vaadin/addons/gridhelpers/GridHelpersDemoView.java

@@ -51,5 +51,6 @@ public GridHelpersDemoView() {
     addDemo(LazyMultiSelectionDemo.class);
     addDemo(CheckboxColumnDemo.class);
     addDemo(EmptyGridLabelDemo.class);
+    addDemo(HeightByRowsDemo.class);
   }
 }

src/test/java/com/flowingcode/vaadin/addons/gridhelpers/HeightByRowsDemo.java

@@ -0,0 +1,49 @@
+/*-
+ * #%L
+ * Grid Helpers Add-on
+ * %%
+ * Copyright (C) 2022 Flowing Code
+ * %%
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * #L%
+ */
+
+package com.flowingcode.vaadin.addons.gridhelpers;
+
+import com.flowingcode.vaadin.addons.demo.DemoSource;
+import com.vaadin.flow.component.grid.Grid;
+import com.vaadin.flow.component.html.Div;
+import com.vaadin.flow.router.PageTitle;
+import com.vaadin.flow.router.Route;
+
+@PageTitle("Height By Rows")
+@DemoSource
+@Route(value = "grid-helpers/height-by-rows", layout = GridHelpersDemoView.class)
+public class HeightByRowsDemo extends Div {
+
+  public HeightByRowsDemo() {
+    setSizeFull();
+
+    Grid<Person> grid = new Grid<>();
+    grid.setItems(TestData.initializeData());
+
+    grid.addColumn(Person::getFirstName).setHeader("First name");
+    grid.addColumn(Person::getLastName).setHeader("Last name");
+    grid.addColumn(Person::getCountry).setHeader("Country");
+
+    GridHelper.setHeightMode(grid, HeightMode.ROW);
+    GridHelper.setHeightByRows(grid, 7);
+
+    add(grid);
+  }
+}