More efficient Char(Int) in common, JS, and JS-IR

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2021 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.
  */
 
@@ -27,4 +27,4 @@ internal fun doubleToInt(a: Double): Int = when {
     else -> jsBitwiseOr(a, 0)
 }
 
-internal fun numberToChar(a: dynamic) = Char(numberToInt(a) and 0xFFFF)
+internal fun numberToChar(a: dynamic) = Char(numberToInt(a).toUShort())