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.

2d/platformer/game_singleplayer.tscn

@@ -12,7 +12,9 @@ script = ExtResource("2")
 [node name="Level" parent="." instance=ExtResource("3")]
 
 [node name="Player" parent="Level" instance=ExtResource("4")]
-position = Vector2(90, 546)
+z_index = 3
+position = Vector2(90, 636.5)
+scale = Vector2(1, 1)
 
 [node name="InterfaceLayer" type="CanvasLayer" parent="."]
 layer = 100

2d/platformer/game_splitscreen.tscn

@@ -55,13 +55,17 @@ render_target_update_mode = 4
 [node name="Player1" parent="Black/SplitContainer/ViewportContainer1/Viewport1" instance=ExtResource("4_8j0va")]
 unique_name_in_owner = true
 modulate = Color(1, 1.5, 2.5, 1)
-position = Vector2(90, 546)
+z_index = 3
+position = Vector2(100, 636.5)
+scale = Vector2(1, 1)
 action_suffix = "_p1"
 
 [node name="Player2" parent="Black/SplitContainer/ViewportContainer1/Viewport1" instance=ExtResource("4_8j0va")]
 unique_name_in_owner = true
 modulate = Color(3, 1, 1, 1)
-position = Vector2(120, 546)
+z_index = 3
+position = Vector2(160, 636.5)
+scale = Vector2(1, 1)
 action_suffix = "_p2"
 
 [node name="ViewportContainer2" type="SubViewportContainer" parent="Black/SplitContainer"]

2d/platformer/player/player.gd

@@ -1,6 +1,7 @@
 class_name Player
 extends CharacterBody2D
 
+@warning_ignore("unused_signal")
 signal coin_collected()
 
 const WALK_SPEED = 300.0

2d/platformer/player/player.tscn

@@ -205,6 +205,7 @@ position = Vector2(0, -14)
 texture = ExtResource("9")
 hframes = 8
 vframes = 8
+frame = 42
 
 [node name="Gun" type="Marker2D" parent="Sprite2D"]
 position = Vector2(14, 1)
@@ -226,6 +227,7 @@ libraries = {
 [node name="Camera" type="Camera2D" parent="."]
 position = Vector2(0, -28)
 offset = Vector2(0, 50)
+process_callback = 0
 limit_left = -715
 limit_top = -250
 limit_right = 1425

2d/platformer/project.godot

@@ -184,6 +184,7 @@ splitscreen={
 
 common/physics_ticks_per_second=120
 2d/default_gravity=2100
+common/physics_interpolation=true
 
 [rendering]