Auto merge of #32134 - jseyfried:forbid_type_alias_as_module, r=nikomatsakis

Forbid glob-importing from a type alias

This PR forbids glob-importing from a type alias or trait (fixes #30560):
```rust
type Alias = ();
use Alias::*; // This is currently allowed but shouldn't be
```

This is a [breaking-change]. Since the disallowed glob imports don't actually import anything, any breakage can be fixed by removing the offending glob import.

r? @alexcrichton

src/test/compile-fail/issue-30560.rs

@@ -0,0 +1,18 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+type Alias = ();
+use Alias::*; //~ ERROR Not a module
+use std::io::Result::*; //~ ERROR Not a module
+
+trait T {}
+use T::*; //~ ERROR items in traits are not importable
+
+fn main() {}