Rollup merge of #114267 - compiler-errors:rpitit-opaque-bounds, r=spastorino
Map RPITIT's opaque type bounds back from projections to opaques An RPITIT in a program's AST is eventually translated into both a projection GAT and an opaque. The opaque is used for default trait methods, like: ``` trait Foo { fn bar() -> impl Sized { 0i32 } } ``` The item bounds for both the projection and opaque are identical, and both have a *projection* self ty. This is mostly okay, since we can normalize this projection within the default trait method body to the opaque, but it does two things: 1. it leads to bugs in places where we don't normalize item bounds, like `deduce_future_output_from_obligations` 2. it leads to extra match arms that are both suspicious looking and also easy to miss This PR maps the opaque type bounds of the RPITIT's *opaque* back to the opaque's self type to avoid this quirk. Then we can fix the UI test for #108304 (1.) and also remove a bunch of match arms (2.). Fixes #108304 r? `@spastorino`
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