Fix incorrect unsupported error on synthetic extension call on LHS of ::

#KT-13271 Fixed

compiler/testData/codegen/box/callableReference/bound/syntheticExtensionOnLHS.kt

@@ -0,0 +1,21 @@
+// WITH_RUNTIME
+// FILE: A.java
+
+public class A {
+    private final String field;
+
+    public A(String field) {
+        this.field = field;
+    }
+
+    public CharSequence getFoo() { return field; }
+}
+
+// FILE: test.kt
+
+fun box(): String {
+    with (A("OK")) {
+        val k = foo::toString
+        return k()
+    }
+}