Move projectiles to layer 2, add enemy mask 2

This moves projectiles to a new collision layer, and adds that layer
to the mask for enemies.

This is to do two things: (1) Prevent lasers from colliding with
themselves ("Huge" and "Double" lasers can overlap), (2) allow enemies
to queue_free themselves, instead of leaving that burden on the projectile

units/enemy.gd

@@ -10,3 +10,6 @@ func _physics_process(delta):
 
 func _on_visible_on_screen_notifier_2d_screen_exited():
 	queue_free()
+
+func _on_area_entered(area):
+	queue_free()

units/enemy.tscn

@@ -1,4 +1,4 @@
-[gd_scene load_steps=4 format=3 uid="uid://4fjgeuv7aun7"]
+[gd_scene load_steps=4 format=3 uid="uid://bdsjg08y1h6yh"]
 
 [ext_resource type="Script" path="res://units/enemy.gd" id="1_6h8a0"]
 [ext_resource type="Texture2D" uid="uid://dqkvsqmwue64p" path="res://units/PNG_Parts&Spriter_Animation/Ship1/Ship1.png" id="1_ndkjl"]
@@ -13,11 +13,13 @@ script = ExtResource("1_6h8a0")
 texture = ExtResource("1_ndkjl")
 
 [node name="Area2D" type="Area2D" parent="."]
+collision_mask = 3
 
 [node name="CollisionShape2D" type="CollisionShape2D" parent="Area2D"]
 position = Vector2(0, -0.75)
 shape = SubResource("RectangleShape2D_mvxux")
 
 [node name="VisibleOnScreenNotifier2D" type="VisibleOnScreenNotifier2D" parent="."]
 
+[connection signal="area_entered" from="Area2D" to="." method="_on_area_entered"]
 [connection signal="screen_exited" from="VisibleOnScreenNotifier2D" to="." method="_on_visible_on_screen_notifier_2d_screen_exited"]

units/projectile.gd

@@ -40,7 +40,6 @@ func _physics_process(delta):
 func _on_area_entered(area):
 	# TODO: apply effects on enemy hit. For now just despawn.
 	queue_free()
-	area.owner.queue_free()
 
 func _integrate_forces(delta):
 	scale = Vector2(100, 100)

units/projectile.tscn

@@ -8,6 +8,7 @@ radius = 4.0
 
 [node name="Projectile" type="Area2D"]
 position = Vector2(68, 1)
+collision_layer = 2
 script = ExtResource("1_t6pyo")
 
 [node name="Sprite2D" type="Sprite2D" parent="."]