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

#KT-6405 Fixed

idea/testData/refactoring/extractFunction/parameters/candidateTypes/flexibleTypesWithNull.kt.after

@@ -7,6 +7,4 @@ fun test() {
     val n = i(property)
 }
 
-private fun i(property: String?): Int? {
-    return property?.length()
-}
+private fun i(property: String?) = property?.length()

idea/testData/refactoring/extractFunction/parameters/candidateTypes/flexibleTypesWithoutNull.kt.after

@@ -7,6 +7,4 @@ fun test() {
     val n = i(property)
 }
 
-private fun i(property: String): Int {
-    return property.length()
-}
+private fun i(property: String) = property.length()

idea/testData/refactoring/extractFunction/parameters/extractThis/explicitLabeledThisInMember.kt.after

@@ -19,6 +19,4 @@ public class A(): Z() {
     }
 }
 
-private fun i(a1: A, b1: A.B): Int {
-    return a1.a + b1.b + a1.z + b1.z
-}
+private fun i(a1: A, b1: A.B) = a1.a + b1.b + a1.z + b1.z

idea/testData/refactoring/extractFunction/parameters/extractThis/explicitThisInExtension.kt.after

@@ -7,6 +7,4 @@ fun Z.foo(): Int {
     return i() + 1
 }
 
-private fun Z.i(): Int {
-    return this.a
-}
+private fun Z.i() = this.a

idea/testData/refactoring/extractFunction/parameters/extractThis/explicitThisInMember.kt.after

@@ -19,6 +19,4 @@ public class A(): Z() {
     }
 }
 
-private fun i(a1: A, b1: A.B): Int {
-    return a1.a + b1.b + b1.z
-}
+private fun i(a1: A, b1: A.B) = a1.a + b1.b + b1.z

idea/testData/refactoring/extractFunction/parameters/extractThis/implicitAndExplicitLabeledThisInMember.kt.after

@@ -19,6 +19,4 @@ public class A(): Z() {
     }
 }
 
-private fun i(a1: A, b1: A.B): Int {
-    return a1.a + b1.b + a1.z + b1.z
-}
+private fun i(a1: A, b1: A.B) = a1.a + b1.b + a1.z + b1.z

idea/testData/refactoring/extractFunction/parameters/extractThis/implicitAndExplicitThisInExtension.kt.after

@@ -7,6 +7,4 @@ fun Z.foo(): Int {
     return i() + 1
 }
 
-private fun Z.i(): Int {
-    return this.a + a
-}
+private fun Z.i() = this.a + a

idea/testData/refactoring/extractFunction/parameters/extractThis/implicitThisInExtension.kt.after

@@ -7,6 +7,4 @@ fun Z.foo(): Int {
     return i() + 1
 }
 
-private fun Z.i(): Int {
-    return a
-}
+private fun Z.i() = a

idea/testData/refactoring/extractFunction/parameters/extractThis/implicitThisInMember.kt.after

@@ -19,6 +19,4 @@ public class A(): Z() {
     }
 }
 
-private fun i(a1: A, b1: A.B): Int {
-    return a1.a + b1.b + b1.z
-}
+private fun i(a1: A, b1: A.B) = a1.a + b1.b + b1.z

idea/testData/refactoring/extractFunction/parameters/extractThis/qualifiedThisAsArgument.kt.after

@@ -9,9 +9,7 @@ class A {
     fun B.foo() = i(this@A, this)
 }
 
-private fun i(a1: A, b: B): Int {
-    return a1.a + b.b
-}
+private fun i(a1: A, b: B) = a1.a + b.b
 
 class B {
     val b = 1

idea/testData/refactoring/extractFunction/parameters/it/innerIt.kt.after

@@ -9,6 +9,4 @@ fun foo(t: Array<Array<Int>>) {
     }
 }
 
-private fun i(it: Int): Int {
-    return it + 1
-}
+private fun i(it: Int) = it + 1

idea/testData/refactoring/extractFunction/parameters/it/lambdaWithIt.kt.after

@@ -9,6 +9,4 @@ fun foo(t: Array<Int>) {
     }
 }
 
-private fun b(t: Array<Int>): Boolean {
-    return t.check { it + 1 > 1 }
-}
+private fun b(t: Array<Int>) = t.check { it + 1 > 1 }

idea/testData/refactoring/extractFunction/parameters/it/outerIt.kt.after

@@ -9,6 +9,4 @@ fun foo(t: Array<Array<Int>>) {
     }
 }
 
-private fun b(it: Array<Int>): Boolean {
-    return it.check { it + 1 > 1 }
-}
+private fun b(it: Array<Int>) = it.check { it + 1 > 1 }

idea/testData/refactoring/extractFunction/parameters/it/simpleIt.kt.after

@@ -9,6 +9,4 @@ fun foo(t: Array<Int>) {
     }
 }
 
-private fun i(it: Int): Int {
-    return it + 1
-}
+private fun i(it: Int) = it + 1

idea/testData/refactoring/extractFunction/parameters/misc/multipleOccurrences.kt.after

@@ -9,6 +9,4 @@ fun foo(a: Int, b: Int, c: Int): Int {
     return i(a, b, c)
 }
 
-private fun i(a: Int, b: Int, c: Int): Int {
-    return (a + b * a - c) + b * c
-}
+private fun i(a: Int, b: Int, c: Int) = (a + b * a - c) + b * c

idea/testData/refactoring/extractFunction/parameters/misc/usagesInCallArgs.kt.after

@@ -13,9 +13,7 @@ public class A() {
     }
 }
 
-private fun i(a: A, t: Int, u: Int, x: Int): Int {
-    return a.bar(t - x, u + x)
-}
+private fun i(a: A, t: Int, u: Int, x: Int) = a.bar(t - x, u + x)
 
 fun foo(a: A, x: Int): Int {
     val t = 10