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

#KT-6405 Fixed

idea/testData/refactoring/extractFunction/delegation/delegationByExpression.kt.after

@@ -8,6 +8,4 @@ class A(a: Int, b: Int): T
 
 class B(a: Int, b: Int): T by A(i(a, b), a - b)
 
-private fun i(a: Int, b: Int): Int {
-    return a + b
-}
+private fun i(a: Int, b: Int) = a + b

idea/testData/refactoring/extractFunction/delegation/delegationByExpressionFull.kt.after

@@ -6,6 +6,4 @@ class A(a: Int, b: Int): T
 
 class B(t: T): T by t(t)
 
-private fun t(t: T): T {
-    return t
-}
+private fun t(t: T) = t

idea/testData/refactoring/extractFunction/delegation/delegationBySuperCall.kt.after

@@ -6,6 +6,4 @@ open class A(a: Int, b: Int)
 
 class B(a: Int, b: Int): A(i(a, b), a - b)
 
-private fun i(a: Int, b: Int): Int {
-    return a + b
-}
+private fun i(a: Int, b: Int) = a + b