C#: Document new `Asinh`, `Acosh` and `Atanh` functions in Mathf

Document on the list of C# api differences the newly exposed

* Mathf.Asinh()
* Mathf.Acosh()
* Mathf.Atanh()

Followup to godotengine/godot#81229

tutorials/scripting/c_sharp/c_sharp_differences.rst

@@ -112,9 +112,12 @@ abs                              Mathf.Abs
 absf                             Mathf.Abs
 absi                             Mathf.Abs
 acos                             Mathf.Acos
+acosh                            Mathf.Acosh
 asin                             Mathf.Asin
+asinh                            Mathf.Asinh
 atan                             Mathf.Atan
 atan2                            Mathf.Atan2
+atanh                            Mathf.Atanh
 bezier_derivative                Mathf.BezierDerivative
 bezier_interpolate               Mathf.BezierInterpolate
 bytes_to_var                     GD.BytesToVar