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.after

@@ -0,0 +1,5 @@
+fun sign(x: Int): Int = when {
+    x < 0 -> -1
+    x > 0 -> 1
+    else -> 0
+}