fix: add mutation lost in slimDOMOptions

[wfk007]

fix: #993

[wfk007]

when using slimDOMOptions in rrweb@1.1.3

Comment width a node.__sn.id === -2 which is exactly the same with IGNORED_NODE

when you getNextId with a Node which is followed by a comment, you will get -2 which is equal to IGNORED_NODE causing the while loop continue, and getNextId will finally return null

but in rrweb@2.0.0-alpha.1, node.__sn.id is dropped by the PR https://github.com/rrweb-io/rrweb/pull/868/files
causing that getNextId will finally return -1 which affect the following judge

[wfk007]

in rrweb@2.0.0-alpha.1, mirror.getId() return -1 may caused by:

1. mutation add: child node may be pushed before its newly added parent, rrweb uses a DoubleLinkedList to store these nodes
2. slimDOMOptions: true, and the Node is an IGNORED_NODE, but not in Mirror

considering case 2:
in rrweb@1.1.3, we can use node.__sn to check whether nextSibling is an IGNORED_NODE
BUT in in rrweb@2.0.0-alpha.1, we can not
because the information with IGNORED_NODE neither in node.__sn nor in Mirror

[wfk007]

before:

before.mov

after fixed:

after.mov

[YunFeng0817]

Thanks for your very nice pull request. The description and solution are very clear and clean.

The failure of Format Check CI can be ignored because it may be caused by the old branch base. I've checked the snapshot.ts and there's no formatting issue.

[wfk007]

@Mark-Fenng @Yuyz0112
Hi, is this pending any other changes?

[YunFeng0817]

Nope, I think everything is good. Just waiting for @Yuyz0112's review.

[Yuyz0112]

sorry for the late