[new feature] CellGroup: add title prop (#2928)

packages/cell-group/index.less

@@ -2,4 +2,11 @@
 
 .van-cell-group {
   background-color: @white;
+
+  &__title {
+    font-size: 14px;
+    padding: 15px 15px 5px;
+    color: @gray-dark;
+    line-height: 16px;
+  }
 }

packages/cell-group/index.tsx

@@ -6,6 +6,7 @@ import { CreateElement, RenderContext } from 'vue/types';
 import { DefaultSlots } from '../utils/use/sfc';
 
 export type CellGroupProps = {
+  title?: string;
   border: boolean
 };
 
@@ -17,7 +18,7 @@ function CellGroup(
   slots: DefaultSlots,
   ctx: RenderContext<CellGroupProps>
 ) {
-  return (
+  const Group = (
     <div
       class={[bem(), { 'van-hairline--top-bottom': props.border }]}
       {...inherit(ctx, true)}
@@ -25,9 +26,21 @@ function CellGroup(
       {slots.default && slots.default()}
     </div>
   );
+
+  if (props.title) {
+    return (
+      <div>
+        <div class={bem('title')}>{props.title}</div>
+        {Group}
+      </div>
+    );
+  }
+
+  return Group;
 }
 
 CellGroup.props = {
+  title: String,
   border: {
     type: Boolean,
     default: true