Improve onEach templates.

Add new functions to reference API.
Add tests for onEach
  #KT-8220

libraries/stdlib/src/generated/_Collections.kt

@@ -1586,6 +1586,14 @@ public inline fun <T> Iterable<T>.none(predicate: (T) -> Boolean): Boolean {
     return true
 }
 
+/**
+ * Performs the given [action] on each element and returns the collection itself afterwards.
+ */
+@SinceKotlin("1.1")
+public inline fun <T, C : Iterable<T>> C.onEach(action: (T) -> Unit): C {
+    return apply { for (element in this) action(element) }
+}
+
 /**
  * Accumulates value starting with the first element and applying [operation] from left to right to current accumulator value and each element.
  */

libraries/stdlib/src/generated/_Maps.kt

@@ -178,6 +178,14 @@ public inline fun <K, V> Map<out K, V>.none(predicate: (Map.Entry<K, V>) -> Bool
     return true
 }
 
+/**
+ * Performs the given [action] on each entry and returns the map itself afterwards.
+ */
+@SinceKotlin("1.1")
+public inline fun <K, V, M : Map<out K, V>> M.onEach(action: (Map.Entry<K, V>) -> Unit): M {
+    return apply { for (element in this) action(element) }
+}
+
 /**
  * Creates an [Iterable] instance that wraps the original map returning its entries when being iterated.
  */

libraries/stdlib/src/generated/_Sequences.kt

@@ -969,6 +969,17 @@ public inline fun <T> Sequence<T>.none(predicate: (T) -> Boolean): Boolean {
     return true
 }
 
+/**
+ * Returns a sequence which performs the given [action] on each element of the original sequence as they pass though it.
+ */
+@SinceKotlin("1.1")
+public fun <T> Sequence<T>.onEach(action: (T) -> Unit): Sequence<T> {
+    return map {
+        action(it)
+        it
+    }
+}
+
 /**
  * Accumulates value starting with the first element and applying [operation] from left to right to current accumulator value and each element.
  */

libraries/stdlib/src/generated/_Strings.kt

@@ -1010,6 +1010,14 @@ public inline fun CharSequence.none(predicate: (Char) -> Boolean): Boolean {
     return true
 }
 
+/**
+ * Performs the given [action] on each character and returns the char sequence itself afterwards.
+ */
+@SinceKotlin("1.1")
+public inline fun <S : CharSequence> S.onEach(action: (Char) -> Unit): S {
+    return apply { for (element in this) action(element) }
+}
+
 /**
  * Accumulates value starting with the first character and applying [operation] from left to right to current accumulator value and each character.
  */