add an any and a union type example for typescript prop annotation (#1121)

Author: gamperl

src/guide/typescript-support.md

@@ -247,13 +247,17 @@ interface Book {
 const Component = defineComponent({
   props: {
     name: String,
+    id: [Number, String],
     success: { type: String },
     callback: {
       type: Function as PropType<() => void>
     },
     book: {
       type: Object as PropType<Book>,
       required: true
+    },
+    metadata: {
+      type: null // metadata is typed as any
     }
   }
 })