Introduce "cascade if" inspection suggesting replacement with when

So #KT-18615 Fixed

idea/testData/inspectionsLocal/cascadeIf/insideOtherIf.kt.after

@@ -0,0 +1,11 @@
+fun println(s: String) {}
+
+fun test(x: Double, a: Boolean, b: Boolean) {
+    if (x > 0.0) {
+        when {
+            a -> println("a")
+            b -> println("b")
+            else -> println("none")
+        }
+    }
+}