Forbid callable references to members and extensions with empty LHS

This syntax is reserved to be likely used in the future as a shorthand for
"this::foo" where the resulting expression doesn't take the receiver as a
parameter but has "this" already bound to it

js/js.translator/testData/callableReference/function/cases/extensionFromClass.kt

@@ -2,7 +2,7 @@
 package foo
 
 class A {
-    fun result() = (::bar)(this, "OK")
+    fun result() = (A::bar)(this, "OK")
 }
 
 fun A.bar(x: String) = x