Rollup merge of #88192 - spastorino:add-tait-test-for-assoc-dyn, r=oli-obk

Use of impl trait in an impl as the value for an associated type in a dyn

r? `@oli-obk`

Related to #86727

src/test/ui/type-alias-impl-trait/type-alias-impl-trait-assoc-dyn.rs

@@ -0,0 +1,12 @@
+// check-pass
+
+#![feature(type_alias_impl_trait)]
+#![allow(dead_code)]
+
+type Foo = Box<dyn Iterator<Item = impl Send>>;
+
+fn make_foo() -> Foo {
+    Box::new(vec![1, 2, 3].into_iter())
+}
+
+fn main() {}