[JS IR] Introduce jsArguments() intrinsic function

`jsArguments()` is lowered into a reference of the `arguments` object.

This is useful for extracting varargs, when calling Kotlin code from
JavaScript. For a concrete example, see KT-15223.

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

@@ -195,6 +195,9 @@ internal fun <A> slice(a: A): A
 @JsIntrinsic
 internal fun unreachable(): Nothing
 
+@JsIntrinsic
+internal fun jsArguments(): Any?
+
 @JsIntrinsic
 @Suppress("REIFIED_TYPE_PARAMETER_NO_INLINE") // TODO: mark `inline` and skip in inliner
 internal fun <reified T : Any> jsClassIntrinsic(): JsClass<T>
@@ -204,4 +207,4 @@ internal fun <reified T : Any> jsClassIntrinsic(): JsClass<T>
 internal fun jsInIntrinsic(lhs: Any?, rhs: Any): Boolean
 
 @JsIntrinsic
-internal fun jsDelete(e: Any?)
+internal fun jsDelete(e: Any?)