Inline variable: fix it works correctly for 'when' subject variable

#KT-29870 Fixed

idea/testData/refactoring/inline/inlineVariableOrProperty/whenSubject.kt

@@ -0,0 +1,7 @@
+fun test(s: String) {
+    when (val x = s.length) {
+        1 -> println("one")
+        2 -> println("two")
+        else -> println(x<caret>)
+    }
+}

idea/testData/refactoring/inline/inlineVariableOrProperty/whenSubject.kt.after

@@ -0,0 +1,7 @@
+fun test(s: String) {
+    when (s.length) {
+        1 -> println("one")
+        2 -> println("two")
+        else -> println(s.length)
+    }
+}