Auto merge of #116891 - aliemjay:opaque-region-infer-rework-2, r=compiler-errors,oli-obk

rework opaque type region inference

User-facing changes are documented in [this comment](rust-lang/rust#116891 (comment)).

The design document is in [this comment](rust-lang/rust#116891 (comment)).

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\- Fix Ice in check_unique; ICE -> Error; fixes #122782.
\- Ignore uncaptured lifetime args; ICE -> Pass; fixes #111906, fixes #110623, fixes #109059, fixes #122307
\- Except equal parameters from the uniqueness check; Pass -> Error; fixes #113916.
\- Check RPITs for invalid args; Pass -> Error; fixes #111935; ICE -> Error; fixes #110726.
\- Rework opaque types region inference; Pass -> Error; fixes #113971, fixes #112841.
\- Reject external lifetimes as invalid args; Pass -> Error; fixes #105498.

r? `@ghost`

Author: bors