Add regression tests for issues marked fixed-by-next-solver (1/N)

[Randl]

Note that while these issues are marked fixed-by-next-solver, some of them also pass with the old solver now.

Fixes #90950
Fixes #102580
Fixes #134312
Fixes #134370
Fixes #141478

LLM disclosure: I used LLM to collect and classify the issues. After that, I manually extracted the MCE from each issue and checked how it failed on older Rust versions.

[rustbot]

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[chenyukang]

Maybe you need to add multiple Fixes #issue_no in PR description to close those issues when PR merged?

[chenyukang]

The same program fails with E0284 on Rust 1.75.0 but passes with the old solver on nightly. Suggest adding current and next revisions preserve both behaviors.

View changes since the review

[Randl]

It fails for me with E0284 with the old solver, both locally and at godbolt. Could it be that you checked with the (default) new solver?

[chenyukang]

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[Randl]

I've added the fixes comment only to tests that pass with both solvers

[Randl]

@rustbot ready