improve rrdom robustness

[YunFeng0817]

To improve the robustness of the virtual-dom implementation imported in #853 and fix some common errors such as #1042

Changes:

1. Add node type check in the diff function
   Now node matching doesn't only rely on the equality of serialized Ids
2. Fix a wired style problem in iframes
   https://rrwebdebug.com/play/index.html?url=https%3A%2F%2Fgist.github.com%2FMark-Fenng%2Fdd95c2246c948ac1bda1c67336210fb1&version=1.0.0-alpha.4&play=on

Thanks for @pdwittig 's really helpful events
This bug is because class selector matching in auto-mounted iframes is case-insensitive.

3. fix [Bug]: Replayer Exception - mutation Failed to execute 'insertBefore' on 'Node': Only one doctype on document allowed #1065 including a test case
4. add afterAppend hook to the diff function
   fix: virtual nodes are passed to plugin's onBuild callback

@bhavitsharma Could you please also review this PR in case I'm missing anything important? Since you have followed some related problems and you are also familiar with the code.

[bhavitsharma]

Sure. Give me a day and I'll get back to ya.

[Juice10]

This is great @Mark-Fenng, much more readable!

[wfk007]

@Mark-Fenng Thanks for your great work andafterAppend hook is really helpful for me to write plugins in the replay.