feat(fontless): support selecting preloaded fonts by subsets

[hi-ogawa]

• Closes [fontless] support selecting preloaded fonts by subsets #649

This PR updated preload option to support selecting preloaded fonts by preload.subsets: [...].

It also updated a public API transformCss to have more flexible preload selection. I added FontFamilyInjectionPluginOptions.filterFontsToPreload and deprecated FontFamilyInjectionPluginOptions.shouldPreload.

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[codecov]

Codecov Report

❌ Patch coverage is 28.57143% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 52.79%. Comparing base (d66809d) to head (12276c7).

Files with missing lines	Patch %	Lines
packages/fontless/src/vite.ts	0.00%	13 Missing ⚠️
packages/fontless/src/utils.ts	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #655      +/-   ##
==========================================
- Coverage   53.40%   52.79%   -0.62%     
==========================================
  Files          11       11              
  Lines         734      752      +18     
  Branches       93       94       +1     
==========================================
+ Hits          392      397       +5     
- Misses        342      355      +13     

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commit: 12276c7

[danielroe]

we might also want to choose preload based on font file extensions (defaulting to only .woff2). maybe we could support just passing a function directly? e.g. preload?: boolean | ((fontFamily: string, data: FontFaceData) => boolean)

[hi-ogawa]

Yes, making it more flexible sounds good to me, but my intention was that subsets based preload selection should provide optional most of the case, so simple option preload.subset might be good enough to start with. Btw, woff (meta.priority = 1) returned by google provider is not a subsetted font, which is why it's large and thus they don't get included in current preload.subsets.

That said, I was also thinking that maybe we can later expand option to { subsets: string[], weights: string[], etc. }, which may become tricky, so I agree with exposing boolean function. However, I think we should also keep simple preload.subsets option.