Update some C# examples for 4.0 (#6693)

* Update some C# examples

- Rename members that have been renamed in Godot's C# API for 4.0.
- Change `delta` parameter type to `double`.
- Ensure parameters match base declaration.
- Other minor code fixes.

---------

Co-authored-by: Paul Joannon <437025+paulloz@users.noreply.github.com>

tutorials/plugins/running_code_in_the_editor.rst

@@ -90,7 +90,7 @@ Here is how a ``_process()`` function might look for you:
 
  .. code-tab:: csharp
 
-    public override void _Process(float delta)
+    public override void _Process(double delta)
     {
         if (Engine.IsEditorHint())
         {
@@ -133,9 +133,9 @@ and open a script, and change it to this:
     [Tool]
     public partial class MySprite : Sprite2D
     {
-        public override void _Process(float delta)
+        public override void _Process(double delta)
         {
-            Rotation += Mathf.Pi * delta;
+            Rotation += Mathf.Pi * (float)delta;
         }
     }
 
@@ -162,15 +162,15 @@ look like this:
 
  .. code-tab:: csharp
 
-    public override void _Process(float delta)
+    public override void _Process(double delta)
     {
         if (Engine.IsEditorHint())
         {
-            Rotation += Mathf.Pi * delta;
+            Rotation += Mathf.Pi * (float)delta;
         }
         else
         {
-            Rotation -= Mathf.Pi * delta;
+            Rotation -= Mathf.Pi * (float)delta;
         }
     }
 
@@ -208,24 +208,23 @@ Add and export a variable speed to the script. The function set_speed after
     [Tool]
     public partial class MySprite : Sprite2D
     {
-        private float speed = 1;
+        private float _speed = 1;
 
         [Export]
-        public float Speed {
-            get => speed;
-            set => SetSpeed(value);
+        public float Speed
+        {
+            get => _speed;
+            set
+            {
+                // Update speed and reset the rotation.
+                _speed = value;
+                Rotation = 0;
+            }
         }
 
-        // Update speed and reset the rotation.
-        private void SetSpeed(float newSpeed)
+        public override void _Process(double delta)
         {
-            speed = newSpeed;
-            Rotation = 0;
-        }
-
-        public override void _Process(float delta)
-        {
-            Rotation += Mathf.Pi * delta * speed;
+            Rotation += Mathf.Pi * (float)delta * speed;
         }
     }