Make all comprehensions keyed, don't rely on LiveComponents

[SteffenDE]

This changes keyed comprehensions to not rely on LiveComponents any more. It is very much work in progress.

TODOs:

• [ ] fix template duplication when rendering new items
• [ ] fix tests that still expect regular comprehensions
• [ ] remove(?) Phoenix.LiveView.Comprehension
• [ ] write more tests
• [ ] write comprehensive documentation about the diff format

[SteffenDE]

cc @josevalim

[SteffenDE]

@josevalim I checked the stream docs and I think they are fine as is. I pushed some other docs changes here: https://github.com/phoenixframework/phoenix_live_view/pull/3865/commits/958343a0c66c2ec6f37b93fd5164493a1b740ec9

[SteffenDE]

I also want to expand the diff documentation a bit when I find the time.

[AlexKovynev]

@SteffenDE not planned for 1.1?

[SteffenDE]

It’s going to be backported to the 1.1 branch and a new RC will ship soon :)