Rollup merge of rust-lang#123962 - oli-obk:define_opaque_types5, r=lcnr

change method resolution to constrain hidden types instead of rejecting method candidates

Some of these are in probes and may affect inference. This is therefore a breaking change.

This allows new code to compile on stable:

```rust
trait Trait {}

impl Trait for u32 {}

struct Bar<T>(T);

impl Bar<u32> {
    fn foo(self) {}
}

fn foo(x: bool) -> Bar<impl Sized> {
    if x {
        let x = foo(false);
        x.foo();
        //^ this used to not find the `foo` method, because while we did equate `x`'s type with possible candidates, we didn't allow opaque type inference while doing so
    }
    todo!()
}
```

r? `@compiler-errors`

fixes  rust-lang#121404

cc rust-lang#116652

Author: fmease

compiler/rustc_hir_typeck/src/callee.rs

@@ -628,7 +628,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 return;
             };
 
-            let pick = self.confirm_method(
+            let pick = self.confirm_method_for_diagnostic(
                 call_expr.span,
                 callee_expr,
                 call_expr,

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -1418,7 +1418,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let impl_ty = self.normalize(span, tcx.type_of(impl_def_id).instantiate(tcx, args));
             let self_ty = self.normalize(span, self_ty);
             match self.at(&self.misc(span), self.param_env).eq(
-                DefineOpaqueTypes::No,
+                DefineOpaqueTypes::Yes,
                 impl_ty,
                 self_ty,
             ) {