[Javascript] Fix syntax error for signed enum (#5503)

* wrap quotes to enum name map to prevent syntax errorn when enum value is negative

* Add a test that covers signed enum case

tests/MyGame/Example/Race.kt

@@ -0,0 +1,16 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+package MyGame.Example
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class Race private constructor() {
+    companion object {
+        const val None: Byte = -1
+        const val Human: Byte = 0
+        const val Dwarf: Byte = 1
+        const val Elf: Byte = 2
+        val names : Array<String> = arrayOf("None", "Human", "Dwarf", "Elf")
+        fun name(e: Int) : String = names[e - None.toInt()]
+    }
+}