Optimize copying large ranges of undefmask blocks

Hopefully fixes #58523

Refactor ppaux out of existence.

A long-time coming, this PR reorganizes and rewrites the pretty-printing architecture of rustc, specifically the parts that involve the typesystem (which used to be in `rustc::util::ppaux`).

*Note: these commits used to be in #57967 before being split off.*

The new API (i.e. the `Printer` and `PrettyPrint` traits) is in `rustc::ty::print`.

Design points, roughly:
* using associated types in `Printer` to allow building e.g. an AST, not just printing as a side-effect
* several overloading points for implementers of `PrettyPrinter`, e.g. how `<...>` is printed
* for `fmt::Display` impls, the value to print is lifted to the `ty::tls` `tcx`, and everything after that stays within the `ty::print` API, which requires `'tcx` to match between values and the printer's `tcx`, without going through `fmt::Display` again

Most of the behavior is unchanged, except for a few details, which should be clear from the test changes.

r? @nikomatsakis

Fixes https://github.com/rust-lang/rust/issues/55464

rustbuild: remove obsolete fulldeps behavior from src/test/pretty tests, and enable them by default.