feat: support variable axis

[qwerzl]

This PR adds support for variable font axis. It's quite sad that AFAIK only Google provides this level of configuration.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 85.00000% with 12 lines in your changes are missing coverage. Please review.

Project coverage is 64.50%. Comparing base (ed5f704) to head (725d358).

Files	Patch %	Lines
playground/pages/providers/google.vue	0.00%	11 Missing ⚠️
src/module.ts	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #141      +/-   ##
==========================================
+ Coverage   63.70%   64.50%   +0.79%     
==========================================
  Files          41       41              
  Lines        2717     2789      +72     
  Branches      397      426      +29     
==========================================
+ Hits         1731     1799      +68     
- Misses        960      966       +6     
+ Partials       26       24       -2     

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[qwerzl]

Hi @danielroe, the type issues are fixed and I've added tests for Recursive. Sorry I didn't see the failed checks yesterday so it took some time.

[danielroe]

Rather than creating a new property (variableAxis) I think we ought to try to use font-variation-settings/variationSettings which could take a string or an object of dimension/value.

We could then use this to render both the font-face and also detect the required variations from CSS directly rather than require it to be configured.

[qwerzl]

@danielroe I've also thought about this, but I'm not sure whether font-variation-settings allows a range of values.