Rollup merge of #145342 - dianne:if-let-super-let, r=nnethercote

fix drop scope for `super let` bindings within `if let`

Fixes rust-lang/rust#145328 by making non-lifetime-extended `super let` reuse the logic used to compute drop scopes for non-lifetime-extended temporaries.

Also fixes rust-lang/rust#145374, which regressed due to rust-lang/rust#143376 introducing `if let`-like scopes for match arms with guards.

Tracking issue for `super let`: rust-lang/rust#139076

This is a regression fix / breaking change for macros stably exposing `super let`, including `pin!` and `format_args!`.
Nominating to be discussed alongside rust-lang/rust#145328: ```@rustbot``` label +I-lang-nominated +I-libs-api-nominated

Author: Zalathar