Refact stdlib generator, add support for different backends

[JS IR BE] Runtime fixes
 * Do not generate external declarations for IR BE
 * Move `arrayToString` helper function out of shared JS stdlib
 * Fix arrays type check for IR BE

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

@@ -65,6 +65,10 @@ private val runtimeSources = listOfKtFilesFrom(
 
     "libraries/stdlib/js/src/kotlin/currentBeMisc.kt",
 
+    // IR BE has its own generated sources
+    "libraries/stdlib/js/src/generated",
+    "libraries/stdlib/js/src/kotlin/collectionsExternal.kt",
+
     // Full version is defined in stdlib
     // This file is useful for smaller subset of runtime sources
     "libraries/stdlib/js/irRuntime/rangeExtensions.kt",

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

@@ -167,6 +167,7 @@ object NashornIrJsTestChecker : AbstractNashornJsTestChecker() {
 
         listOf(
             BasicBoxTest.TEST_DATA_DIR_PATH + "nashorn-polyfills.js",
+            "libraries/stdlib/js/src/js/polyfills.js",
             "js/js.translator/testData/out/irBox/testRuntime.js"
         ).forEach(engine::loadFile)
 

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/BoxJsTestGenerated.java

@@ -7558,6 +7558,11 @@ public class BoxJsTestGenerated extends AbstractBoxJsTest {
             runTest("js/js.translator/testData/box/standardClasses/arraySize.kt");
         }
 
+        @TestMetadata("arraySort.kt")
+        public void testArraySort() throws Exception {
+            runTest("js/js.translator/testData/box/standardClasses/arraySort.kt");
+        }
+
         @TestMetadata("arraysIterator.kt")
         public void testArraysIterator() throws Exception {
             runTest("js/js.translator/testData/box/standardClasses/arraysIterator.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/IrBoxJsTestGenerated.java

@@ -7558,6 +7558,11 @@ public class IrBoxJsTestGenerated extends AbstractIrBoxJsTest {
             runTest("js/js.translator/testData/box/standardClasses/arraySize.kt");
         }
 
+        @TestMetadata("arraySort.kt")
+        public void testArraySort() throws Exception {
+            runTest("js/js.translator/testData/box/standardClasses/arraySort.kt");
+        }
+
         @TestMetadata("arraysIterator.kt")
         public void testArraysIterator() throws Exception {
             runTest("js/js.translator/testData/box/standardClasses/arraysIterator.kt");