Modularize Discord RPC (#247)

This commit delegates all Discord-related functions to DiscordManager.gd and adds a project setting bool to toggle using Discord RPC at all. Toggling off will reduce cpu and memory overhead when Discord is not needed.

Scripts/Classes/Singletons/DiscordManager.gd

@@ -0,0 +1,63 @@
+extends Node
+
+var enabled: bool = ProjectSettings.get_setting("application/use_discord", false) and not (OS.has_feature("linux") and OS.has_feature("arm64"))
+var rpc = null
+
+class DiscordRPCStub:
+	var app_id
+	var start_timestamp
+	var details
+	var state
+	var large_image
+	var small_image
+
+	func start(): pass
+	func refresh(): pass
+	func get_is_discord_working() -> bool: return false
+	func shutdown(): pass
+
+func _ready() -> void:
+	if enabled:
+		rpc = Engine.get_singleton("DiscordRPC")
+	else:
+		rpc = DiscordRPCStub.new()
+	setup_discord_rpc()
+	
+func _process(_delta: float) -> void:
+	if enabled:
+		rpc.run_callbacks()
+
+func setup_discord_rpc() -> void:
+	if not enabled:
+		return
+	rpc.app_id = 1331261692381757562
+	rpc.start_timestamp = int(Time.get_unix_time_from_system())
+	rpc.details = "In Title Screen.."
+	if rpc.get_is_discord_working():
+		rpc.refresh()
+
+func set_discord_status(details: String = "") -> void:
+	if not enabled:
+		return
+	rpc.details = details
+	if rpc.get_is_discord_working():
+		rpc.refresh()
+
+func update_discord_status(details: String) -> void:
+	if not enabled:
+		return
+	rpc.details = details
+	rpc.state = details
+	rpc.large_image = (Global.level_theme + Global.theme_time).to_lower()
+	rpc.small_image = Global.current_campaign.to_lower()
+	if rpc.get_is_discord_working():
+		rpc.refresh()
+
+func refresh_discord_rpc() -> void:
+	if not enabled:
+		return
+	if not rpc.get_is_discord_working():
+		return
+	Global.update_game_status()
+	update_discord_status("")
+	rpc.refresh()