Introduce 'when' subject: consider equality right-hand side as subject candidate

idea/testData/codeInsight/codeTransformations/branched/when/introduceSubject/whenWithMultipleConditionTypes.kt

@@ -5,6 +5,7 @@ fun test(n: Int): String {
         n in 10..100 -> "average"
         n in 100..1000 -> "big"
         n == 1000000 -> "million"
+        2000000 == n -> "two millions"
         n !in -100..-10 -> "good"
         n is Int -> "unknown"
         else -> "unknown"

idea/testData/codeInsight/codeTransformations/branched/when/introduceSubject/whenWithMultipleConditionTypes.kt.after

@@ -5,6 +5,7 @@ fun test(n: Int): String {
         in 10..100 -> "average"
         in 100..1000 -> "big"
         1000000 -> "million"
+        2000000 -> "two millions"
         !in -100..-10 -> "good"
         is Int -> "unknown"
         else -> "unknown"

idea/testData/codeInsight/codeTransformations/branched/when/introduceSubject/whenWithSwappedEqualityTests.kt

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

idea/testData/codeInsight/codeTransformations/branched/when/introduceSubject/whenWithSwappedEqualityTests.kt.after

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