add support for `System.ComponentModel.DescriptionAttribute`

[FroggieFrog]

Similar to #11 it would be nice to add support for the System.ComponentModel.DescriptionAttribute.
At least I use it far more often than the System.ComponentModel.DataAnnotations.DisplayAttribute.

example:

enum MyValues
{
    /// <summary>
    /// The first value.
    /// </summary>
    [Description("This is value 1.")]
    Value1,
	/// <summary>
    /// This is an alternative to Value1.
    /// </summary>
    [Description("An alternative value.")]
    Value2
}

[andrewlock]

That seems reasonable to me! As in #11, I'm not entirely sure what the support should look like. Should it only affect ToStringFast()? Or should we use it for Parse and IsDefined etc too? 🤔 What are your thoughts @FroggieFrog?

[FroggieFrog]

I don't really have an opinion on that topic, but what I'm regularly using is a combination of custom extension methods to parse forth and back. (e.g. string ToDescription() and T ParseByDescription<T>())
But I would recommend to be consistent with the implementation in #11. (What ever that would be.)

[eglauko]

I have always used DescriptionAttribute instead of DisplayNameAttribute.
It would be nice to have both options, if there is [DisplayName], it generates the GetDisplayName() and FromDisplayName(string) methods, and if there is [Description] it generates the GetDescription() and FromDescription(string) methods.
I just wouldn't use the approach described in #11, I would do something like this:

=> value switch
{
  Colour.Red => "The red description"
  Colour.Blue => "The blue description"
  Colour.Green => nameof(Colour.Green), // when not having the attribute,
  _ => value.ToString()
}

[adamradocz]

I don't think it's a good idea to return the ToString value of the enum when you specifically asked for the Description or the DisplayName.
What about this:

string GetDescription(Color color) => color switch
{
    Color.Red => "The red description",
    Color.Blue => "The blue description",
    _ => string.Empty,
};

Or:

bool GetDescription(Color color, out string description)
{
    switch (color)
    {
        case Color.Red:
            description = "The red description";
            return true;
        case Color.Blue:
            description = "The blue description";
            return true;
        default:
            description = string.Empty;
            return false;
    }
}