Test that borrows of projections are promoted everywhere

Previously, this worked in `fn`s but not `const`s or `static`s.

src/test/ui/consts/promote_borrowed_field.rs

@@ -0,0 +1,12 @@
+// run-pass
+
+// From https://github.com/rust-lang/rust/issues/65727
+
+const _: &i32 = {
+    let x = &(5, false).0;
+    x
+};
+
+fn main() {
+    let _: &'static i32 = &(5, false).0;
+}