add collecting coins

scripts/game_manager.gd

@@ -0,0 +1,18 @@
+class_name GM
+extends Node
+
+var player_state = {
+	"coins": 0,
+}
+
+func add_coins(amount: int) -> void:
+	player_state["coins"] += amount
+
+func set_coins(amount: int) -> void:
+	player_state["coins"] = amount
+
+func get_coins() -> int:
+	return player_state["coins"]
+
+func remove_coins(amount: int) -> void:
+	player_state["coins"] -= amount