Provide string-to-number conversions in JS and common stdlib.

Relates to #KT-8286
#KT-4497 Fixed

js/js.libraries/test/core/testUtils.kt

@@ -19,4 +19,7 @@ package kotlin.test
 public fun assertTypeEquals(expected: Any?, actual: Any?) {
     //TODO: find analogue
     //assertEquals(expected?.javaClass, actual?.javaClass)
-}
+}
+
+internal inline fun String.removeLeadingPlusOnJava6(): String = this
+internal fun doubleTotalOrderEquals(a: Double?, b: Double?) = a == b || (a != a && b != b)