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/convertToExpressionBody/multipleStatements.kt

@@ -0,0 +1,6 @@
+// PROBLEM: none
+
+fun foo(): String {
+    val v = 1
+    <caret>return "abc"
+}