[JS_IR] Use new plugin to build Kotlin/JS stdlib with IR compiler

- Switch to building stdlib with bootstrap compiler since IR is stable
  enough
- Build stdlib with coreLibs by default
- Include JS IR stdlib to kotlin distribution

libraries/stdlib/wasm/runtime/testHelpers.kt

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * 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
+
+import kotlin.wasm.internal.wasm_unreachable
+
+fun assertEquals(x: Boolean, y: Boolean) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Byte, y: Byte) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Short, y: Short) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Char, y: Char) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Int, y: Int) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Long, y: Long) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Float, y: Float) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Double, y: Double) {
+    if (x != y) wasm_unreachable()
+}
+
+
+fun assertEquals(x: Boolean, y: Boolean, s: String) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Byte, y: Byte, s: String) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Short, y: Short, s: String) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Char, y: Char, s: String) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Int, y: Int, s: String) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Long, y: Long, s: String) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Float, y: Float, s: String) {
+    if (x != y) wasm_unreachable()
+}
+fun assertEquals(x: Double, y: Double, s: String) {
+    if (x != y) wasm_unreachable()
+}