[Feature Request] Add variable font support

[geirolafs]

Is your feature request related to a problem? Please describe.
I work with variable fonts regularly but Font Manager can't preview or explore their axes.

Describe the solution you'd like

• Detect and identify variable fonts
• Show available axes (weight, width, slant, etc.) with sliders
• Real-time preview as axes values change
• Display axis ranges (min/max/default)

Describe alternatives you've considered
Currently I have to activate the font in Font Manager, then switch to Figma to explore the variable axes. Having this integrated in Font Manager would be much more convenient when evaluating multiple variable fonts.

Additional context
Variable fonts are standard (Inter, Roboto Flex, system fonts like SF Pro and Segoe UI Variable) in Google Fonts, system fonts, and web development - a single variable font file can replace multiple static font files.

GTK's GtkFontChooser already supports font variations via GTK_FONT_CHOOSER_LEVEL_VARIATIONS flag (see GTK blog post), which could potentially simplify implementation.

I'd be happy to help test or contribute to this feature.

[JerryCasiano]

This has been on the "TODO" list for quite a while now, it's unfortunately a very low priority for me. It's just not something that I believe the majority of users will even use.

If it's something that you're interested in and willing to work on that would certainly accelerate the process and be more than welcome. Let me know if there's anything I can help with in that regard.

[geirolafs]

@JerryCasiano Thanks for adding this to the 2.0 milestone! I completely understand the priority consideration.

I have a setup that's working okay for me (using Figma for the variable axes exploration), so this isn't urgent on my end. There might be a skill issue on my part 😄 but I'll definitely look into this when I get some time.

If I do work on it, I'd probably focus on:

1. Detection + display of available variable axes and their ranges
2. Sliders to manipulate the axes

I'll keep you posted if I make any progress.