Rollup merge of #136310 - lqd:long-types, r=compiler-errors

normalize `*.long-type.txt` paths for compare-mode tests

When using a compare mode, the name of the test + compare-mode is embedded in some of rustc's output, like the location where a long type `bla.long-type(-some-hash)?.txt` is written to. That generally makes these tests fail under all compare-modes.

This PR fixes this by normalizing the compare-mode suffix away in the stderr output. We can also see some remnants of the long-removed `nll` compare mode being normalized away ^^.

I did this to fix some failures with `--compare-mode next-solver` (but it also fixes them with e.g. `--compare-mode polonius` of course):
- it makes 9 new tests pass with the new solver
- however, 3 tests I changed here still don't pass with the new solver (IIRC there were 2 ICEs, and some duplicate errors for the 3rd one)

(There was also one that triggered slowness in the new solver while triggering the long type failure, I'll mention this on zulip. )

Author: jhpratt