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

#KT-6405 Fixed

idea/testData/refactoring/extractFunction/initializers/functions/localFunction.kt.after

@@ -3,9 +3,7 @@
 // PARAM_DESCRIPTOR: value-parameter val a: kotlin.Int defined in bar.foo
 // PARAM_DESCRIPTOR: value-parameter val b: kotlin.Int defined in bar.foo
 fun bar(n: Int) {
-    fun i(a: Int, b: Int): Int {
-        return a + b - n
-    }
+    fun i(a: Int, b: Int) = a + b - n
 
     fun foo(a: Int, b: Int) = i(a, b) - 1
 }

idea/testData/refactoring/extractFunction/initializers/functions/localFunctionWithLambda.kt.after

@@ -3,9 +3,7 @@
 // PARAM_DESCRIPTOR: value-parameter val a: kotlin.Int defined in bar.foo
 // PARAM_DESCRIPTOR: value-parameter val b: kotlin.Int defined in bar.foo
 fun bar(n: Int) {
-    fun i(a: Int, b: Int): Int {
-        return a + b - n
-    }
+    fun i(a: Int, b: Int) = a + b - n
 
     fun foo(a: Int, b: Int) = { i(a, b) - 1 }.invoke()
 }

idea/testData/refactoring/extractFunction/initializers/functions/memberFunction.kt.after

@@ -5,7 +5,5 @@
 class A(val n: Int) {
     fun foo(a: Int, b: Int) = i(a, b) - 1
 
-    private fun i(a: Int, b: Int): Int {
-        return a + b - n
-    }
+    private fun i(a: Int, b: Int) = a + b - n
 }

idea/testData/refactoring/extractFunction/initializers/functions/memberFunctionParameters.kt.after

@@ -3,7 +3,5 @@
 class A(val n: Int) {
     fun foo(a: Int, b: Int = i(a)) = a + b - n - 1
 
-    private fun i(a: Int): Int {
-        return a + n
-    }
+    private fun i(a: Int) = a + n
 }

idea/testData/refactoring/extractFunction/initializers/functions/memberFunctionParametersWithLambda.kt.after

@@ -3,7 +3,5 @@
 class A(val n: Int) {
     fun foo(a: Int, b: Int = { i(a) }.invoke()) = a + b - n - 1
 
-    private fun i(a: Int): Int {
-        return a + n
-    }
+    private fun i(a: Int) = a + n
 }

idea/testData/refactoring/extractFunction/initializers/functions/memberFunctionWithLambda.kt.after

@@ -5,7 +5,5 @@
 class A(val n: Int) {
     fun foo(a: Int, b: Int) = { i(a, b) - 1 }.invoke()
 
-    private fun i(a: Int, b: Int): Int {
-        return a + b - n
-    }
+    private fun i(a: Int, b: Int) = a + b - n
 }

idea/testData/refactoring/extractFunction/initializers/functions/topLevelFunction.kt.after

@@ -4,6 +4,4 @@
 // PARAM_DESCRIPTOR: value-parameter val b: kotlin.Int defined in foo
 fun foo(a: Int, b: Int) = i(a, b) - 1
 
-private fun i(a: Int, b: Int): Int {
-    return a + b
-}
+private fun i(a: Int, b: Int) = a + b

idea/testData/refactoring/extractFunction/initializers/functions/topLevelFunctionParameters.kt.after

@@ -3,6 +3,4 @@
 val n = 1
 fun foo(a: Int, b: Int = i(a)) = a + b - 1
 
-private fun i(a: Int): Int {
-    return a + n
-}
+private fun i(a: Int) = a + n

idea/testData/refactoring/extractFunction/initializers/functions/topLevelFunctionParametersWithLambda.kt.after

@@ -3,6 +3,4 @@
 val n = 1
 fun foo(a: Int, b: Int = { i(a) }) = a + b - 1
 
-private fun i(a: Int): Int {
-    return a + n
-}
+private fun i(a: Int) = a + n

idea/testData/refactoring/extractFunction/initializers/functions/topLevelFunctionWithLambda.kt.after

@@ -4,6 +4,4 @@
 // PARAM_DESCRIPTOR: value-parameter val b: kotlin.Int defined in foo
 fun foo(a: Int, b: Int) = { i(a, b) - 1 }.invoke()
 
-private fun i(a: Int, b: Int): Int {
-    return a + b
-}
+private fun i(a: Int, b: Int) = a + b