Texture handling rewrite

[MrKev312]

PR Classification

Code cleanup and functionality improvements.

PR Summary

Refactored and enhanced image processing and texture conversion in the JustDanceEditor project.

• Namespace and Import Adjustments: Replaced SwitchTexture with TextureConverter and updated using directives.
• Image Processing Enhancements: Added image resizing and new background handling methods in CoachesLargeBundleGenerator.cs and CoverArtGenerator.cs.
• Functionality Improvements: Updated MenuArtConverter.cs and PictoConverter.cs to use new texture conversion methods.
• Dependency Updates: Added SixLabors.Fonts and SixLabors.ImageSharp.Drawing packages.
• Added support for GTX File Format.