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/diagnostics/tests/callableReference/function/innerConstructorFromClass.kt

@@ -6,10 +6,9 @@ class A {
     inner class Inner
     
     fun main() {
-        val x = ::Inner
+        ::<!CALLABLE_REFERENCE_TO_MEMBER_OR_EXTENSION_WITH_EMPTY_LHS!>Inner<!>
         val y = A::Inner
 
-        checkSubtype<KFunction1<A, A.Inner>>(x)
         checkSubtype<KFunction1<A, Inner>>(y)
     }