Auto merge of rust-lang#102570 - cjgillot:deagg-debuginfo, r=oli-obk

Perform simple scalar replacement of aggregates (SROA) MIR opt

This is a re-open of rust-lang#85796

I copied the debuginfo implementation (first commit) from `@eddyb's` own SROA PR.

This pass replaces plain field accesses by simple locals when possible.
To be eligible, the replaced locals:
- must not be enums or unions;
- must not be used whole;
- must not have their address taken.

The storage and deinit statements are duplicated on each created local.

cc `@tmiasko` who reviewed the former version of this PR.

Author: bors