Codegen for callable reference expressions

#KT-1183 In Progress

compiler/testData/codegen/box/callableReference/classMemberFromTopLevelStringNoArgs.kt

@@ -0,0 +1,8 @@
+class A {
+    fun foo() = "OK"
+}
+
+fun box(): String {
+    val x = A::foo
+    return A().x()
+}