ImportOptimizer: add cases for unresolved references

Part of #KT-31331

idea/testData/editor/optimizeImports/common/IteratorFunction.kt

@@ -1,5 +1,6 @@
 import test1.MyClass
 import test1.iterator
+import test2.iterator
 
 fun foo() {
     val s = MyClass()

idea/testData/editor/optimizeImports/common/IteratorFunction2.kt

@@ -0,0 +1,11 @@
+import test1.MyClass
+import test1.iterator
+import test2.iterator
+import test3.notIterator
+import test1.invoke
+import test4.*
+
+fun foo() {
+    val s = MyClass()
+    for (i in s) {}
+}

idea/testData/editor/optimizeImports/common/IteratorFunction2.kt.after

@@ -0,0 +1,10 @@
+import test1.MyClass
+import test1.invoke
+import test1.iterator
+import test2.iterator
+import test4.*
+
+fun foo() {
+    val s = MyClass()
+    for (i in s) {}
+}