Introduce "use expression body" inspection #KT-16063 Fixed

Converted from the relevant intention
Reported cases: one-liners, whens
Also, more exact caret detection in local inspection tests

idea/testData/inspectionsLocal/useExpressionBody/when.kt

@@ -0,0 +1,7 @@
+fun sign(x: Int): Int {
+    <caret>return when {
+        x < 0 -> -1
+        x > 0 -> 1
+        else -> 0
+    }
+}