Add in-memory image support and contextual help to RibbonExtensions

[magsonleone]

Summary of the Pull Request

What is this about: Add in-memory image support and contextual help to RibbonExtensions

Description:

This PR introduces new features and improvements to the Ribbon extensions for Revit:

• New in-memory image support
  • Added SetImage(Bitmap) and SetLargeImage(Bitmap) methods to apply 16x16 and 32x32 icons directly from System.Drawing.Bitmap.
  • Automatic conversion to WPF BitmapSource, enabling runtime or embedded resource icons.
• Simplified contextual help
  • Added SetContextualHelp(string url) method to quickly associate documentation or support pages with Ribbon buttons.
• Technical updates
  • Added System.Drawing.Common dependency to the project.
  • Introduced ConvertToImageSource() helper for safe and efficient GDI+ to WPF conversion.

These additions make Revit UI customization more flexible and dynamic, supporting both runtime-generated icons and integrated online help.

Quality Checklist

• [ x ] My code follows the style guidelines of this project
• [ x ] I have performed a self-review of my own code
• [ x ] My changes generate no new warnings