Remove old and unused project settings, update various demos for 4.2 (#1024)

- Move all demo projects that don't require Forward+/Mobile-only features
  to the Compatibility rendering method. This improves performance significantly
  on low-end devices and ensures visuals are identical to a web export
  of the demo.
- Set deadzone on all inputs to 0.2 for better gamepad usability.
- Remove reliance on `default_env.tres` to use built-in Environment
  resources in the main scene instead (which follows the preview environment
  workflow).
- Remove notices pointing to GDNative or VisualScript, since both were
  removed in 4.0.
- Various bug fixes and usability tweaks to 10+ demos.

networking/websocket_multiplayer/scene/combo.tscn

@@ -23,44 +23,12 @@ columns = 2
 
 [node name="Main" parent="GridContainer" instance=ExtResource("2_reiiv")]
 layout_mode = 2
-anchors_preset = 0
-anchor_right = 0.0
-anchor_bottom = 0.0
-offset_right = 574.0
-offset_bottom = 322.0
-grow_horizontal = 1
-grow_vertical = 1
 
 [node name="Main2" parent="GridContainer" instance=ExtResource("2_reiiv")]
 layout_mode = 2
-anchors_preset = 0
-anchor_right = 0.0
-anchor_bottom = 0.0
-offset_left = 578.0
-offset_right = 1152.0
-offset_bottom = 322.0
-grow_horizontal = 1
-grow_vertical = 1
 
 [node name="Main3" parent="GridContainer" instance=ExtResource("2_reiiv")]
 layout_mode = 2
-anchors_preset = 0
-anchor_right = 0.0
-anchor_bottom = 0.0
-offset_top = 326.0
-offset_right = 574.0
-offset_bottom = 648.0
-grow_horizontal = 1
-grow_vertical = 1
 
 [node name="Main4" parent="GridContainer" instance=ExtResource("2_reiiv")]
 layout_mode = 2
-anchors_preset = 0
-anchor_right = 0.0
-anchor_bottom = 0.0
-offset_left = 578.0
-offset_top = 326.0
-offset_right = 1152.0
-offset_bottom = 648.0
-grow_horizontal = 1
-grow_vertical = 1