[Feature] Add a string method for `OpenURL` and `SetGamepadMappings`

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• The issue is specific to Raylib-cs and not raylib
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• My code has no errors or misuse of Raylib-cs

Issue description

Hello, i saw by the methods OpenURL and SetGamepadMappings that there is just a method that takes sbyte* i would suggest to do a second method with a string value.

And i found another thing, you could use instead of try/finally:

You use:

    public static unsafe int MeasureText(string text, int fontSize)
    {
      UTF8Buffer utF8Buffer = text.ToUTF8Buffer();
      try
      {
        return Raylib.MeasureText(utF8Buffer.AsPointer(), fontSize);
      }
      finally
      {
        utF8Buffer.Dispose();
      }
    }

What i suggest:

    public static unsafe int MeasureText(string text, int fontSize)
    {
        using (UTF8Buffer buffer = text.ToUTF8Buffer())
        {
            return Raylib.MeasureText(buffer.AsPointer(), fontSize);
        }
    }

What i suggest (smallest):

    public static unsafe int MeasureText(string text, int fontSize) {
        using UTF8Buffer buffer = text.ToUTF8Buffer();
        return Raylib.MeasureText(buffer.AsPointer(), fontSize);
    }

That would Dispose it to and it would smaller.

[9ParsonsB]

We are more then happy to accept pull requests, though we already use your suggested method:

https://github.com/ChrisDill/Raylib-cs/blob/master/Raylib-cs/types/Raylib.Utils.cs#L886

[MrScautHD]

Merged: https://github.com/ChrisDill/Raylib-cs/pull/180