Add NSFontAssetRequest implementation

[gcasa]

This PR provides an implementation of NSFontAssetRequest.

The test for this is here:

https://github.com/gcasa/NSFontAssetRequest_test

[gcasa]

@fredkiefer I have tested this and it is working. Please take a look and let me know if it is acceptable.

[gcasa]

@fredkiefer Please review when ready. This is tested and working. The font is properly added (at least the ones I have tested).

[fredkiefer]

I am going on a two week holiday trip right now and won't have the time to review this properly. If you want a quick review, feel free to ask @rfm .

[gcasa]

I am going on a two week holiday trip right now and won't have the time to review this properly. If you want a quick review, feel free to ask @rfm .

Okay. Have a nice trip. :)

[gcasa]

@rfm Please take a look. I have addressed @fredkiefer 's latest comments.

[rfm]

I'm away from home for the next week and a half, and don't think I'll be able to look at this until I'm back.

[Copilot]

Pull Request Overview

This PR implements NSFontAssetRequest, a class for downloading and installing font assets dynamically. The implementation provides a complete font downloading system with support for CSS-based font URLs (like Google Fonts), direct font file URLs, and cross-platform font installation.

• Implements NSFontAssetRequest with progress tracking and completion handlers
• Adds GSFontAssetDownloader as a pluggable backend for font downloading and installation
• Integrates font cache refresh notifications to update the font panel when new fonts are installed

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
Source/NSFontAssetRequest.m	Complete implementation of NSFontAssetRequest class with download orchestration
Source/GSFontAssetDownloader.m	New font downloading backend with CSS parsing, validation, and installation
Source/NSFontManager.m	Adds font cache refresh method with notification support
Source/NSFontPanel.m	Integrates font manager notifications to refresh panel when fonts change
Source/GSFontInfo.m	Adds font cache refresh functionality to font enumerator
Headers/AppKit/NSFontAssetRequest.h	Header updates with GNUstep extensions
Headers/Additions/GNUstepGUI/GSFontAssetDownloader.h	New header for font downloader class
Headers/AppKit/NSProgressIndicator.h	Adds modern style constants for compatibility
Headers/AppKit/NSFontManager.h	Adds private method and notification declarations
Headers/Additions/GNUstepGUI/GSFontInfo.h	Adds refreshFontCache method declaration
Source/GNUmakefile	Updates build system to include new GSFontAssetDownloader files

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[gcasa]

The NSFontAssetRequest_test has evolved into something akin to Font Book.app on macOS.

[gcasa]

I think this one is ready to merge @rfm and @fredkiefer. Please review and let me know.