Add regression test for scala#6384

Fixed by 18ce5d2 in scala#6467

tests/pos/i6384.scala

@@ -0,0 +1,15 @@
+trait Tc1[A]
+trait Tc2[A]
+
+class X
+object X {
+  implicit def catchAll[F[_]]: F[X] = ???
+}
+
+type ManualLambda[a] = Tc1[a] & Tc2[a]
+
+object app extends App {
+  implicitly[Tc1[X]] //ok
+  implicitly[ManualLambda[X]] // ok
+  implicitly[Tc1[X] & Tc2[X]] // no implicit argument of type Tc1[X] & Tc2[X] was found for parameter ev of method implicitly in object DottyPredef
+}