Add test case

Author: OlivierBlanvillain

tests/pos/11463.scala

@@ -0,0 +1,11 @@
+type LeafElem[X] = X match
+   case String => Char
+   case Array[t] => LeafElem[t]
+   case Iterable[t] => LeafElem[t]
+   case AnyVal => X
+
+def leafElem[X](x: X): LeafElem[X] = x match
+   case x: String      => x.charAt(0)
+   case x: Array[t]    => leafElem(x(9))
+   case x: Iterable[t] => leafElem(x.head)
+   case x: AnyVal      => x