Undo unnecessary changes to stdlib

Partially revert "[stdlib] Reduce usage of extension functions"

js/js.tests/test/org/jetbrains/kotlin/js/test/JsIrTestRuntime.kt

@@ -99,7 +99,7 @@ private val fullRuntimeSources = listOfKtFilesFrom(
 
     // Full version is defined in stdlib
     // This file is useful for smaller subset of runtime sources
-    "libraries/stdlib/js/irRuntime/rangeExtensions.kt",
+    "libraries/stdlib/js/irRuntime/smallRuntimeMissingDeclarations.kt",
 
     // Mostly array-specific stuff
     "libraries/stdlib/js/src/kotlin/builtins.kt",
@@ -158,6 +158,8 @@ val reducedRuntimeSources = fullRuntimeSources - listOfKtFilesFrom(
     "libraries/stdlib/src/kotlin/util/KotlinVersion.kt",
     "libraries/stdlib/src/kotlin/util/Tuples.kt",
     "libraries/stdlib/common/src/generated/_Comparisons.kt"
+) + listOfKtFilesFrom(
+    "libraries/stdlib/js/irRuntime/smallRuntimeMissingDeclarations.kt"
 )
 
 private fun listOfKtFilesFrom(vararg paths: String): List<String> {

libraries/stdlib/js/irRuntime/smallRuntimeMissingDeclarations.kt

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin
+
+/**
+ * Returns `true` if this char sequence is empty (contains no characters).
+ */
+@kotlin.internal.InlineOnly
+public inline fun CharSequence.isEmpty(): Boolean = length == 0
+
+/**
+ * Accumulates value starting with [initial] value and applying [operation] from left to right to current accumulator value and each element.
+ */
+public inline fun <T, R> Array<out T>.fold(initial: R, operation: (acc: R, T) -> R): R {
+    var accumulator = initial
+    for (element in this) accumulator = operation(accumulator, element)
+    return accumulator
+}

libraries/stdlib/src/kotlin/coroutines/CoroutineContextImpl.kt

@@ -98,7 +98,7 @@ internal class CombinedContext(
 
     override fun toString(): String =
         "[" + fold("") { acc, element ->
-            if (acc.length == 0) element.toString() else "$acc, $element"
+            if (acc.isEmpty()) element.toString() else "$acc, $element"
         } + "]"
 
     private fun writeReplace(): Any {
@@ -116,11 +116,6 @@ internal class CombinedContext(
             private const val serialVersionUID: Long = 0L
         }
 
-        private fun readResolve(): Any {
-            var result: CoroutineContext = EmptyCoroutineContext
-            for (element in elements)
-                result = result + element
-            return result
-        }
+        private fun readResolve(): Any = elements.fold(EmptyCoroutineContext, CoroutineContext::plus)
     }
 }

libraries/stdlib/src/kotlin/util/Standard.kt

@@ -135,7 +135,7 @@ public inline fun <T> T.takeUnless(predicate: (T) -> Boolean): T? {
 public inline fun repeat(times: Int, action: (Int) -> Unit) {
     contract { callsInPlace(action) }
 
-    for (index in 0 .. (times - 1)) {
+    for (index in 0 until times) {
         action(index)
     }
 }