Rollup merge of #140713 - compiler-errors:check_ref_cast, r=lcnr

Structurally resolve in `check_ref_cast` in new solver

Fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/203

r? lcnr

tests/ui/cast/cast-alias-of-array-to-element.rs

@@ -0,0 +1,22 @@
+//@ check-pass
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
+// Regression test for <https://github.com/rust-lang/trait-system-refactor-initiative/issues/203>.
+// Test that we structually normalize in the hacky `&[T; N] -> *const T` in cast.
+
+trait Mirror {
+    type Assoc: ?Sized;
+}
+impl<T: ?Sized> Mirror for T {
+    type Assoc = T;
+}
+
+struct W<'a>(&'a <[f32; 0] as Mirror>::Assoc);
+
+fn foo(x: W<'_>) -> *const f32 {
+    x.0 as *const f32
+}
+
+fn main() {}