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

#KT-6405 Fixed

idea/testData/refactoring/extractFunction/basic/localExtraction.kt.after

@@ -1,8 +1,6 @@
 fun foo(a: Int): Int {
     // SIBLING:
-    fun i(): Int {
-        return a + 10
-    }
+    fun i() = a + 10
 
     return i()
 }

idea/testData/refactoring/extractFunction/basic/noConflictWithInnerFunction.kt.after

@@ -1,9 +1,7 @@
 fun foo() {
     val a = 1
     // SIBLING:
-    fun b1(): Boolean {
-        return a > 0
-    }
+    fun b1() = a > 0
 
     if (b1()) {
         fun b(): Int { return 0 }

idea/testData/refactoring/extractFunction/basic/traitFunction.kt.after

@@ -3,7 +3,5 @@ trait T{
         return i()
     }
 
-    fun i(): Int {
-        return 1
-    }
+    fun i() = 1
 }