update zh-cn/application-dev/reference/arkui-ts/ts-offscreencanvasrenderingcontext2d.md.
文档中，多处示例排版有误，导致，大多数示例代码混乱，已修复；
Signed-off-by: N小桂子家滴 <hjy920712@163.com>
Signed-off-by: N小桂子家滴 <hjy920712@163.com>