Auto merge of rust-lang#102618 - aliemjay:simplify-closure-promote, r=compiler-errors

rework applying closure requirements in borrowck

Previously the promoted closure constraints were registered under the category `ConstraintCategory::ClosureBounds` in `type_check::prove_closure_bounds()` and then mapped back their original category in `regions_infer::best_blame_constraint` using the complicated map `closure_bounds_mapping`.

Now we're registering promoted constraints under their original category and span earlier in `type_check::prove_closure_bounds`.

See commit messages.

Fixes rust-lang#99245

Author: bors