🔬 move to universe-based lifetimes

[nikomatsakis]

rustc currently uses a "leak-check"-based system for handling higher-ranked bounds. This design has a few flaws (e.g. #33684), and doesn't scale well to quantification over types and other things. @sgrif has been exploring moving to an alternate system, which I am dubbing the "universe" system. This is the system used by chalk.

The currently implementation is in these two PRs:

#47861
#48407

This issue exists to track the move for now.

[nikomatsakis]

Implemented in #55517