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/keepComments/1.kt

@@ -0,0 +1,3 @@
+fun getText(): String {
+    <caret>return "xxx" //TODO
+}

idea/testData/inspectionsLocal/useExpressionBody/convertToExpressionBody/keepComments/1.kt.after

@@ -0,0 +1 @@
+fun getText(): String = "xxx" //TODO

idea/testData/inspectionsLocal/useExpressionBody/convertToExpressionBody/keepComments/2.kt

@@ -0,0 +1,4 @@
+fun getText(): String {
+    // let's return xxx
+    <caret>return "xxx" //TODO
+}

idea/testData/inspectionsLocal/useExpressionBody/convertToExpressionBody/keepComments/2.kt.after

@@ -0,0 +1,2 @@
+fun getText(): String = // let's return xxx
+        "xxx" //TODO

idea/testData/inspectionsLocal/useExpressionBody/convertToExpressionBody/keepComments/3.kt

@@ -0,0 +1,3 @@
+fun getText(): String { // let's return xxx
+    <caret>return "xxx"
+}

idea/testData/inspectionsLocal/useExpressionBody/convertToExpressionBody/keepComments/3.kt.after

@@ -0,0 +1,2 @@
+fun getText(): String = // let's return xxx
+        "xxx"

idea/testData/inspectionsLocal/useExpressionBody/convertToExpressionBody/keepComments/4.kt

@@ -0,0 +1,4 @@
+fun getText(): String {
+    /* let's return xxx */
+    <caret>return "xxx" /* TODO */
+}

idea/testData/inspectionsLocal/useExpressionBody/convertToExpressionBody/keepComments/4.kt.after

@@ -0,0 +1,2 @@
+fun getText(): String = /* let's return xxx */
+        "xxx" /* TODO */