Reorganize stdlib-js sources specific to the current JS backend

Move kotlin-stdlib-js project and the sources specific to the current backend to 'stdlib/js-v1' directory,
but leave sources that can be shared with the new IR backend in the common 'stdlib/js' location
with exception for 'stdlib/js/src/generated', which is used exclusively for current backend.
This simplifies sourceset configuration when building stdlib with the new backend.

libraries/stdlib/js-ir/runtime/numberConversion.kt

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2010-2018 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.js
+
+fun numberToByte(a: dynamic): Byte = toByte(numberToInt(a))
+
+fun numberToDouble(a: dynamic): Double = js("+a").unsafeCast<Double>()
+
+fun numberToInt(a: dynamic): Int = if (a is Long) a.toInt() else doubleToInt(a)
+
+fun numberToShort(a: dynamic): Short = toShort(numberToInt(a))
+
+// << and >> shifts are used to preserve sign of the number
+fun toByte(a: dynamic): Byte = js("a << 24 >> 24").unsafeCast<Byte>()
+fun toShort(a: dynamic): Short = js("a << 16 >> 16").unsafeCast<Short>()
+
+fun numberToLong(a: dynamic): Long = if (a is Long) a else fromNumber(a)
+
+fun toLong(a: dynamic): Long = fromInt(a)
+
+fun doubleToInt(a: dynamic) = js("""
+    if (a > 2147483647) return 2147483647;
+    if (a < -2147483648) return -2147483648;
+    return a | 0;
+""").unsafeCast<Int>()
+
+fun numberToChar(a: dynamic) = Char(numberToInt(a) and 0xFFFF)