Rewrite the pipes compiler

[brson]

It is written in an old dialect of Rust, targets the old runtime and has been very difficult to maintain because it generates code that relies on a number of language and library features.

Related to #7666, #7667

[huonw]

Triage: As referenced by the multitude of closed bugs linked above, the old version was entirely removed in #8170. This isn't stopping a rewrite, of course.

(Tagged as A-an-interesting-project.)

[emberian]

Pipes are gone.