Replace 'if' with 'when': don't swallow comments if there is no synthetic else branch

#KT-34640 Fixed

idea/testData/intentions/branched/ifWhen/ifToWhen/doNotSwallowComment.kt

@@ -0,0 +1,12 @@
+fun test(foo: String) {
+    <caret>if (foo == "1") {
+        println("1")
+    }
+
+    if (foo == "a") {
+        // some comments for "a"
+        println("a");
+    }
+}
+
+fun println(s: String) {}

idea/testData/intentions/branched/ifWhen/ifToWhen/doNotSwallowComment.kt.after

@@ -0,0 +1,14 @@
+fun test(foo: String) {
+    when (foo) {
+        "1" -> {
+            println("1")
+        }
+    }
+
+    if (foo == "a") {
+        // some comments for "a"
+        println("a");
+    }
+}
+
+fun println(s: String) {}