Rollup merge of rust-lang#71103 - samrat:tait-sized, r=estebank

Add test case for type aliasing `impl Sized`

Fixes rust-lang#71085

Author: Dylan-DPC

src/test/ui/type-alias-impl-trait/type-alias-impl-trait-sized.rs

@@ -0,0 +1,17 @@
+// check-pass
+
+#![feature(type_alias_impl_trait)]
+
+type A = impl Sized;
+fn f1() -> A { 0 }
+
+type B = impl ?Sized;
+fn f2() -> &'static B { &[0] }
+
+type C = impl ?Sized + 'static;
+fn f3() -> &'static C { &[0] }
+
+type D = impl ?Sized;
+fn f4() -> &'static D { &1 }
+
+fn main() {}