Split or glue together checks for not null and is instance + more intelligent use of filter vs filterTo

#KT-14284 Fixed
 #KT-14286 Fixed
 #KT-14287 Fixed
 #KT-14303 Fixed

idea/testData/intentions/loopToCallChain/introduceIndex/indexWithNestedLoop.kt

@@ -1,6 +1,6 @@
 // WITH_RUNTIME
-// INTENTION_TEXT: "Replace with 'flatMap{}.filterNot{}.mapIndexedTo(){}'"
-// INTENTION_TEXT_2: "Replace with 'asSequence().flatMap{}.filterNot{}.mapIndexedTo(){}'"
+// INTENTION_TEXT: "Replace with 'flatMap{}.filter{}.mapIndexedTo(){}'"
+// INTENTION_TEXT_2: "Replace with 'asSequence().flatMap{}.filter{}.mapIndexedTo(){}'"
 fun foo(list: List<String>, target: MutableCollection<Int>) {
     var i = 0
     <caret>for (s in list) {