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.

compute/texture/README.md

@@ -7,7 +7,7 @@ When the mouse cursor is above the plane you can "draw" on the plane to drive th
 
 Language: GDScript
 
-Renderer: Forward Plus
+Renderer: Forward+
 
 > Note: this demo requires Godot 4.2 or later
 

compute/texture/project.godot

@@ -12,7 +12,7 @@ config_version=5
 
 config/name="TestCustomTextures"
 run/main_scene="res://main.tscn"
-config/features=PackedStringArray("4.2", "Forward Plus")
+config/features=PackedStringArray("4.2")
 config/icon="res://icon.svg"
 
 [rendering]