Transform 'if' to 'when' with subject if possible

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithEqualityTests.kt.after

@@ -1,8 +1,8 @@
 fun test(n: Int): String {
-    return <caret>when {
-        n == 0 -> "zero"
-        n == 1 -> "one"
-        n == 2 -> "two"
+    return <caret>when (n) {
+        0 -> "zero"
+        1 -> "one"
+        2 -> "two"
         else -> "unknown"
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithIs.kt.after

@@ -1,8 +1,8 @@
 fun test(obj: Any): String {
-    return <caret>when {
-        obj is String -> "string"
-        obj is Int -> "int"
-        obj is Class<*> -> "class"
+    return <caret>when (obj) {
+        is String -> "string"
+        is Int -> "int"
+        is Class<*> -> "class"
         else -> "unknown"
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithNegativeIs.kt.after

@@ -1,8 +1,8 @@
 fun test(obj: Any): String {
-    return <caret>when {
-        obj !is Iterable<*> -> "not iterable"
-        obj !is Collection<*> -> "not collection"
-        obj !is MutableCollection<*> -> "not mutable collection"
+    return <caret>when (obj) {
+        !is Iterable<*> -> "not iterable"
+        !is Collection<*> -> "not collection"
+        !is MutableCollection<*> -> "not mutable collection"
         else -> "unknown"
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithNegativeRangeTests.kt.after

@@ -1,8 +1,8 @@
 fun test(n: Int): String {
-    return <caret>when {
-        n !in 0..1000 -> "unknown"
-        n !in 0..100 -> "big"
-        n !in 0..10 -> "average"
+    return <caret>when (n) {
+        !in 0..1000 -> "unknown"
+        !in 0..100 -> "big"
+        !in 0..10 -> "average"
         else -> "small"
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithRangeTests.kt.after

@@ -1,8 +1,8 @@
 fun test(n: Int): String {
-    return <caret>when {
-        n in 0..10 -> "small"
-        n in 10..100 -> "average"
-        n in 100..1000 -> "big"
+    return <caret>when (n) {
+        in 0..10 -> "small"
+        in 10..100 -> "average"
+        in 100..1000 -> "big"
         else -> "unknown"
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithRangeTestsAndMultiConditions.kt.after

@@ -1,8 +1,8 @@
 fun test(n: Int): String {
-    return <caret>when {
-        n in 0..5, n in 5..10 -> "small"
-        n in 10..50, n in 50..100 -> "average"
-        n in 100..500, n in 500..1000 -> "big"
+    return <caret>when (n) {
+        in 0..5, in 5..10 -> "small"
+        in 10..50, in 50..100 -> "average"
+        in 100..500, in 500..1000 -> "big"
         else -> "unknown"
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/ifWithRangeTestsAndUnparenthesizedMultiConditions.kt.after

@@ -1,8 +1,8 @@
 fun test(n: Int): String {
-    return <caret>when {
-        n in 0..5, n in 5..10 -> "small"
-        n in 10..50, n in 50..100 -> "average"
-        n in 100..500, n in 500..1000 -> "big"
+    return <caret>when (n) {
+        in 0..5, in 5..10 -> "small"
+        in 10..50, in 50..100 -> "average"
+        in 100..500, in 500..1000 -> "big"
         else -> "unknown"
     }
 }

idea/testData/codeInsight/codeTransformations/branched/ifWhen/ifToWhen/whenWithMultipleConditionTypes.kt.after

@@ -1,12 +1,12 @@
 fun test(n: Int): String {
-    return <caret>when {
-        n !is Int -> "???"
-        n in 0..10 -> "small"
-        n in 10..100 -> "average"
-        n in 100..1000 -> "big"
-        n == 1000000 -> "million"
-        n !in -100..-10 -> "good"
-        n is Int -> "unknown"
+    return <caret>when (n) {
+        !is Int -> "???"
+        in 0..10 -> "small"
+        in 10..100 -> "average"
+        in 100..1000 -> "big"
+        1000000 -> "million"
+        !in -100..-10 -> "good"
+        is Int -> "unknown"
         else -> "unknown"
     }
 }