[FIR] KT-58284: Prevent missing diagnostics on for loops

^KT-58284 Fixed

compiler/testData/diagnostics/tests/missingIteratorMissing.kt

@@ -0,0 +1,8 @@
+// FIR_IDENTICAL
+// ISSUE: KT-58284
+
+fun foo() {
+    for (i in <!ITERATOR_MISSING!>0<!>) {}
+}
+
+fun String.iterator(): Iterator<Int> = TODO()