Auto merge of #123720 - amandasystems:dyn-enable-refactor, r=nikomatsakis

Rewrite handling of universe-leaking placeholder regions into outlives constraints

This commit prepares for Polonius by moving handling of leak check/universe errors out of the inference step by rewriting any universe error into an outlives-static constraint.

This variant is a work in progress but seems to pass most tests.

Note that a few debug assertions no longer hold; a few extra eyes on those changes are appreciated!

Author: bors