Add more Gradient related functionality (wishlist)

[nhmkdev]

Support

• Gradient configuration in the UI (!) 💯
• Gradient for shapes
• Multi-point gradients
• Customizable interpolation
• Support Gamma correction option
• FormattedText support

References:

• https://learn.microsoft.com/en-us/dotnet/desktop/winforms/advanced/how-to-create-a-path-gradient?view=netframeworkdesktop-4.8
• https://learn.microsoft.com/en-us/dotnet/desktop/winforms/advanced/how-to-apply-gamma-correction-to-a-gradient?view=netframeworkdesktop-4.8

[MarkVabulas]

I created PR #135 which implements the gradients, but I'm not sure if you were looking for a toggleable way. I don't think anyone using this particular functionality would ever want for them to be disabled. I can confirm that the output on my system makes things look much cleaner, as well.