Add test for generic bounds on associated types

This was fixed in 1e9af9f but it seems
that a test was never added.

Closes #4315

Author: ayazhafiz

tests/source/where-clause.rs

@@ -56,3 +56,8 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
         // ...
     }
 }
+
+// #4315
+pub trait AsUnindented {
+    type Output<'ast> where Self: 'ast;
+}

tests/target/where-clause.rs

@@ -105,3 +105,8 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
         // ...
     }
 }
+
+// #4315
+pub trait AsUnindented {
+    type Output<'ast> where Self: 'ast;
+}