Add some new tests on functions and extension functions

compiler/testData/codegen/boxWithJava/reflection/functionReferenceErasedToKFunction/K.kt

@@ -0,0 +1,13 @@
+class K {
+    fun reverse(s: String): String {
+        return s.reverse()
+    }
+
+    companion object {
+        fun getRef() = K::reverse
+    }
+}
+
+fun box(): String {
+    return J.go()
+}