Add type-as-type-param test

Author: maple

tests/ui/impl-trait/type-as-type-param.rs

@@ -0,0 +1 @@
+impl<Y<A, B, C>> Z for X<T> {} //~ ERROR: expected type parameter, found path `Y<A, B, C>`

tests/ui/impl-trait/type-as-type-param.stderr

@@ -0,0 +1,18 @@
+error: expected type parameter, found path `Y<A, B, C>`
+ --> $DIR/type-as-type-param.rs:1:6
+ |
+LL | impl<Y<A, B, C>> Z for X<T> {}
+ | ^^^^^^^^^^ expected type parameter, found path
+ |
+help: you might have meant to bind a type parameter to a trait
+ |
+LL | impl<T: Y<A, B, C>> Z for X<T> {}
+ | ++
+help: alternatively, you might have meant to bind type parameters to trait `Y`
+ |
+LL - impl<Y<A, B, C>> Z for X<T> {}
+LL + impl<A: Y, B: Y, C: Y> Z for X<T> {}
+ |
+
+error: aborting due to 1 previous error
+