Rollup merge of #121570 - Nilstrieb:!copy, r=clubby789

Make most bootstrap step types !Copy

This makes all bootstrap types except for `Compiler` and `TargetSelection` `!Copy`. This makes it easier to modify them by adding !Copy types in the future, something that `@saethlin` has complained about before, and comes at no cost of code clarity, the impls were completely unused.

Making `Compiler` and `TargetSelection` `!Copy` (which would allow getting rid of interning) is highly nontrivial as they are used and copied **all over the place**. This should hopefully get most of the benefits.

Author: matthiaskrgr