Allow const enum to be visible to TypeScript

[singpolyma]

Instead of just using number type could generate a TypeScript-side const enum like hxtsdgen does

[benmerckx]

Do you have an example of what you'd consider a const enum in Haxe? https://haxe.org/manual/types-abstract-enum.html?

[singpolyma]

For example this:

enum abstract MessageDirection(Int) {
	var MessageReceived;
	var MessageSent;
}

with hxtsdgen gives me this:

export namespace snikket {
	export const enum MessageDirection {
		MessageReceived = 0,
		MessageSent = 1,
	}
}

so that I can reference the enum items by name in typescript instead of needing to use the raw numbers.