feature: add an API entry for mergeProps (#817)

Author: skirtles-code

src/api/global-api.md

@@ -451,3 +451,26 @@ const app = createApp({
 ```
 
 **See also**: [`$nextTick` instance method](instance-methods.html#nexttick)
+
+## mergeProps
+
+Takes multiple objects containing VNode props and merges them into a single object. A newly created object is returned, the objects passed as arguments are not modified.
+
+Any number of objects can be passed, with properties from later arguments taking precedence. Event listeners are handled specially, as are `class` and `style`, with the values of these properties being merged rather than overwritten.
+
+```js
+import { h, mergeProps } from 'vue'
+
+export default {
+  inheritAttrs: false,
+
+  render() {
+    const props = mergeProps({
+      // The class will be merged with any class from $attrs
+      class: 'active'
+    }, this.$attrs)
+
+    return h('div', props)
+  }
+}
+```