`Vec::append` but by value

[Ratatouille]

Weird syntax idea(s) for UMCS

As a user of rust (as opposed to a developer on rust itself), this would be very nice. One use case where I ran into this was when using itertools. Specially the intersperse method from itertools. There is an unstable intersperse method in the std iterator trait. If I don't use the fully qualified name for the itertools intersperse I got a warning (forget if it was clippy or rustc). If I do use the fully qualified name, I can't use the chain of method calls (i.e. a.iter().something(...).intersp…