Add e2e test for MaxLengthPlugin

[im-adithya]

Adds e2e for #2255

lexical-.3.mp4

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Name	Status	Preview	Updated
lexical	✅ Ready (Inspect)	Visit Preview	May 30, 2022 at 0:19AM (UTC)
lexical-playground	✅ Ready (Inspect)	Visit Preview	May 30, 2022 at 0:19AM (UTC)

[zurfyx]

Thank you, additional stuff you can test:

1. Selection
2. Pasting text on an empty/non-empty editor
3. IME on boundaries
4. Emojis (that can have variable size)

[im-adithya]

Thanks for the inputs @zurfyx! This helped me find a bug(?) in MaxLengthPlugin.
I'm not quite sure because I don't exactly know how emojis work in lexical. As far as the issue is concerned, it is as follows:

lexical-.4.mp4

1. Type any random 30 characters
2. Copy this emoji 💏 or any other emoji of length 2 (occupying a length of 2, otherwise this emoji is actually of length 11 as shown by '💏'.length which also can be an error if lexical is supposed to treat this as an 11-length emoji, but a....a💏 (28 as) works fine in MaxLength)
3. Remove a character and paste the emoji at the end (and ONLY at the end, otherwise the behavior is proper)

The entire editor gets cleared and the Block Format dropdown disappears! (I've found out that it is because the blockType of editor gets changed to root after being cleared)

I would like to work on this after getting to know a bit more about emoji guidelines as that would help in a better understanding of the functionality!