Auto merge of #57344 - petrochenkov:regreach, r=arielb1

privacy: Fix regression in impl reachability

Rollback to pre-https://github.com/rust-lang/rust/pull/56878 logic of determining reachability.
`reachability(impl Trait<Substs> for Type<Substs>) = reachability(Trait & Type)`, substs are ignored.

Fixes https://github.com/rust-lang/rust/issues/57264

src/test/ui/privacy/auxiliary/issue-57264-1.rs

@@ -0,0 +1,9 @@
+mod inner {
+    pub struct PubUnnameable;
+}
+
+pub struct Pub<T>(T);
+
+impl Pub<inner::PubUnnameable> {
+    pub fn pub_method() {}
+}

src/test/ui/privacy/auxiliary/issue-57264-2.rs

@@ -0,0 +1,10 @@
+mod inner {
+    pub struct PubUnnameable;
+
+    impl PubUnnameable {
+        pub fn pub_method(self) {}
+    }
+}
+
+pub trait PubTraitWithSingleImplementor {}
+impl PubTraitWithSingleImplementor for Option<inner::PubUnnameable> {}

src/test/ui/privacy/issue-57264-1.rs

@@ -0,0 +1,8 @@
+// compile-pass
+// aux-build:issue-57264-1.rs
+
+extern crate issue_57264_1;
+
+fn main() {
+    issue_57264_1::Pub::pub_method();
+}

src/test/ui/privacy/issue-57264-2.rs

@@ -0,0 +1,10 @@
+// compile-pass
+// aux-build:issue-57264-2.rs
+
+extern crate issue_57264_2;
+
+fn infer<T: issue_57264_2::PubTraitWithSingleImplementor>(arg: T) -> T { arg }
+
+fn main() {
+    infer(None).unwrap().pub_method();
+}