Add "unnecessary local variable" inspection #KT-15958 Fixed

idea/testData/inspectionsLocal/unnecessaryVariable/varCopy.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+
+fun sqrPlusOne(arg: Int): Int {
+    var <caret>other = arg
+    other++
+    return other * other
+}