Extraction Engine: Generate function/property accessor with expression body (whenever applicable)

#KT-6405 Fixed

idea/testData/refactoring/introduceProperty/extractWithGetterToFile.kt.after

@@ -2,9 +2,7 @@
 val n: Int = 1
 
 private val i: Int
-    get() {
-        return n + 1
-    }
+    get() = n + 1
 
 fun foo(): Int {
     return i