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/lambdaIfUnit.kt

@@ -0,0 +1,12 @@
+// IS_APPLICABLE: true
+
+fun <T> run(f: () -> T) = f()
+fun whenExpr(flag: Boolean) {
+    <caret>run {
+        println("run")
+        if (flag) {
+            println("flag")
+        }
+    }
+}
+fun println(s: String) {}