Improve the description of【beforeCreate】

[Nicklaus6]

https://vuejs.org/api/options-lifecycle.html#beforecreate

Called immediately when the instance is initialized, after props resolution, before processing other options such as data() or computed.

After reading the source code, I find the description on the document is some ambiguous and can lead to misunderstanding. Because initState is called after beforeCreate called, and initProps is called in the initState, which means the props resolution is before beforeCreate but the props initialization if after that. In initProps, the props are defined as reactive properties.

Thus, I hope the document can be clearer and more accurate, helping users to better learn and use Vue.