Iterate Intention: Fix detection of extension iterators

#KT-8616 Fixed

idea/testData/intentions/iterateExpression/extensionIteratorWithPartialSubstitution1.kt.after

@@ -0,0 +1,10 @@
+// WITH_RUNTIME
+class T<U, V>
+
+operator fun <X> T<X, String>.iterator(): Iterator<X> = listOf<X>().iterator()
+
+fun test() {
+    for (i in T<Int, String>()) {
+        <caret>
+    }
+}