coercions reviews/misc whatevers

[BoxyUwU]

Fixes #132765 "remove normalize call" in theory breaking as we might now treat some previously-ambig hr aliases as rigid when we shouldn't. we may want to explicitly normalize the coercion target in fcx.coerce like the new solver does

wip misc stuff from while i'm reviewing/reading through this logic

r? ghost

[rust-log-analyzer]

The job tidy failed! Check out the build log: (web) (plain enhanced) (plain)

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fmt: checked 6467 files
tidy check
tidy [rustdoc_json (src)]: `rustdoc-json-types` modified, checking format version
tidy: Skipping binary file check, read-only filesystem
tidy [style (tests)]: /checkout/tests/ui/coercion/hr_alias_normalization_leaking_vars.rs:7: trailing whitespace
tidy [style (tests)]: FAIL
removing old virtual environment
creating virtual environment at '/checkout/obj/build/venv' using 'python3.10' and 'venv'
creating virtual environment at '/checkout/obj/build/venv' using 'python3.10' and 'virtualenv'
Requirement already satisfied: pip in ./build/venv/lib/python3.10/site-packages (25.2)
linting python files
---
info: ES-Check: there were no ES version matching errors!  🎉
typechecking javascript files
tidy: The following check failed: style (tests)
Bootstrap failed while executing `test src/tools/tidy tidyselftest --extra-checks=py,cpp,js,spellcheck`
Command `/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools-bin/rust-tidy /checkout /checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo /checkout/obj/build 4 /node/bin/npm --extra-checks=py,cpp,js,spellcheck` failed with exit code 1
Created at: src/bootstrap/src/core/build_steps/tool.rs:1549:23
Executed at: src/bootstrap/src/core/build_steps/test.rs:1280:29

Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:03:24
  local time: Sat Oct 11 00:03:42 UTC 2025
  network time: Sat, 11 Oct 2025 00:03:42 GMT
##[error]Process completed with exit code 1.
Post job cleanup.