Refactor gameplay menus into owned scenes

ui/menus/ModalMenu.gd

@@ -0,0 +1,24 @@
+extends Control
+
+signal closed
+
+@onready var close_button: Control = get_node_or_null("CloseButton")
+
+
+func _ready() -> void:
+	visible = false
+	if close_button != null and close_button.has_signal("pressed"):
+		close_button.pressed.connect(close_menu)
+
+
+func open_menu() -> void:
+	visible = true
+
+
+func close_menu() -> void:
+	visible = false
+	closed.emit()
+
+
+func handle_unhandled_input(_event: InputEvent) -> bool:
+	return visible