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

compiler/testData/codegen/boxInline/callableReference/classLevel2.2.kt

@@ -3,9 +3,9 @@ package test
 class A(val z: Int) {
     fun calc() = z
 
-    fun test() = call(A(z), ::calc)
+    fun test() = call(A(z), A::calc)
 }
 
 inline fun call(p: A, s: A.() -> Int): Int {
     return p.s()
-}
+}