Enable physics interpolation in all 2D demos (#1070)

This makes uses of the new built-in 2D physics interpolation
added in 4.3.

For 3D demos, a separate PR requiring `master` will be made later.

networking/multiplayer_bomber/project.godot

@@ -75,6 +75,10 @@ set_bomb={
 ]
 }
 
+[physics]
+
+common/physics_interpolation=true
+
 [rendering]
 
 renderer/rendering_method="gl_compatibility"

networking/multiplayer_bomber/world.tscn

@@ -303,6 +303,7 @@ text = "EXIT GAME"
 
 [node name="Camera2D" type="Camera2D" parent="."]
 offset = Vector2(512, 300)
+process_callback = 0
 
 [node name="PlayerSpawner" type="MultiplayerSpawner" parent="."]
 _spawnable_scenes = PackedStringArray("res://player.tscn")