Rollup merge of #144875 - scottmcm:more-mir-tests, r=cjgillot

Add some pre-codegen MIR tests for debug mode

No functional changes; just some tests.

I made these for rust-lang/rust#144483, but that's going in a different direction, so I wanted to propose we just add them to help see the impact of other related changes in the future.

r? mir

Author: Zalathar