add layoutWeight to avoid Image from going out of FlowItem

Signed-off-by: Nzcdqs <junfeng.lijunfeng@huawei.com>
Change-Id: Iba2121decb28e8d15c81c74a6f3d79d048d62933

zh-cn/application-dev/reference/arkui-ts/ts-container-waterflow.md

@@ -260,6 +260,8 @@ struct WaterflowDemo {
               Text("N" + item).fontSize(12).height('16')
               Image('res/waterFlowTest(' + item % 5 + ').jpg')
                 .objectFit(ImageFit.Fill)
+                .width('100%')
+                .layoutWeight(1)
             }
           }
           .width(this.itemWidthArray[item])