Merge #3964 #3965 #3967

Merge #3964 #3965 #3967

3964: Nicer Chalk debug logs r=matklad a=flodiebold

I'm looking at a lot of Chalk debug logs at the moment, so here's a few changes to make them slightly nicer...

3965: Implement inline associated type bounds r=matklad a=flodiebold

Like `Iterator<Item: SomeTrait>`.

This is an unstable feature, but it's used in the standard library e.g. in the definition of Flatten, so we can't get away with not implementing it :)

(This is cherry-picked from my recursive solver branch, where it works better, but I did manage to write a test that works with the current Chalk solver as well...)

3967: Handle `Self::Type` in trait definitions when referring to own associated type r=matklad a=flodiebold

It was implemented for other generic parameters for the trait, but not for `Self`.

(Last one off my recursive solver branch :smile: )

Co-authored-by: Florian Diebold <flodiebold@gmail.com>