Rollup merge of #90417 - lcnr:stabilize-relaxed-struct-unsizing, r=wesleywiser

stabilize `relaxed_struct_unsize`

closes #81793

the fcp is already complete.

src/test/ui/feature-gates/feature-gate-relaxed_struct_unsize.rs

@@ -1,10 +0,0 @@
-// Test that we allow unsizing even if there is an unchanged param in the
-// field getting unsized.
-struct A<T, U: ?Sized + 'static>(T, B<T, U>);
-struct B<T, U: ?Sized>(T, U);
-
-fn main() {
-    let x: A<[u32; 1], [u32; 1]> = A([0; 1], B([0; 1], [0; 1]));
-    let y: &A<[u32; 1], [u32]> = &x; //~ ERROR mismatched types
-    assert_eq!(y.1.1.len(), 1);
-}

src/test/ui/feature-gates/feature-gate-relaxed_struct_unsize.stderr

@@ -1,14 +0,0 @@
-error[E0308]: mismatched types
-  --> $DIR/feature-gate-relaxed_struct_unsize.rs:8:34
-   |
-LL |     let y: &A<[u32; 1], [u32]> = &x;
-   |            -------------------   ^^ expected slice `[u32]`, found array `[u32; 1]`
-   |            |
-   |            expected due to this
-   |
-   = note: expected reference `&A<[u32; 1], [u32]>`
-              found reference `&A<[u32; 1], [u32; 1]>`
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0308`.

src/test/ui/unsized/unchanged-param.rs

@@ -1,4 +1,3 @@
-#![feature(relaxed_struct_unsize)]
 // run-pass
 // Test that we allow unsizing even if there is an unchanged param in the
 // field getting unsized.