[JS BE] Support passing an array as argument of vararg in named form

#KT-38059 fixed

compiler/testData/codegen/box/vararg/kt37779.kt

@@ -1,7 +1,11 @@
 // !LANGUAGE: +AllowAssigningArrayElementsToVarargsInNamedFormForFunctions
-// IGNORE_BACKEND: JS
 
-fun test(vararg s: String) = s[1]
+fun test(vararg s: String) = s[1] + s.size
 
-fun box(): String =
-    test(s = arrayOf("", "OK"))
+fun box(): String {
+    val r = test(s = arrayOf("aaa", "Bb"))
+
+    if (r != "Bb2") return "fail: $r"
+
+    return "OK"
+}