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/boxWithStdlib/reflection/properties/privateToThisAccessors.kt

@@ -1,3 +1,4 @@
+import kotlin.reflect.*
 import kotlin.reflect.jvm.*
 
 class K<in T : String> {
@@ -6,10 +7,10 @@ class K<in T : String> {
         set(value) {}
 
     fun run(): String {
-        val p = ::t
+        val p = K::class.memberProperties.single() as KMutableProperty1<K<String>, String>
         p.isAccessible = true
-        p.set(this, "" as T)
-        return p.get(this)
+        p.set(this as K<String>, "")
+        return p.get(this) as String
     }
 }