Auto merge of #15695 - canaltinova:stylo-font-face, r=Manishearth
Auto merge of #15695 - canaltinova:stylo-font-face, r=Manishearth

Stylo: Add constructors for @font-face descriptors

<!-- Please describe your changes on the following line: -->
Part of https://bugzilla.mozilla.org/show_bug.cgi?id=1340728

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix [Bug #1340728](https://bugzilla.mozilla.org/show_bug.cgi?id=1340728)

<!-- Either: -->
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/15695)
<!-- Reviewable:end -->

larsbergstrom/servo,pyfisch/servo,rnestler/servo,splav/servo,splav/servo,upsuper/servo,paulrouget/servo,szeged/servo,CJ8664/servo,szeged/servo,fiji-flo/servo,fiji-flo/servo,sadmansk/servo,canaltinova/servo,szeged/servo,emilio/servo,szeged/servo,peterjoel/servo,jimberlage/servo,rnestler/servo,szeged/servo,larsbergstrom/servo,peterjoel/servo,larsbergstrom/servo,ConnorGBrewster/servo,jimberlage/servo,DominoTree/servo,eddyb/servo,ConnorGBrewster/servo,KiChjang/servo,saneyuki/servo,peterjoel/servo,saneyuki/servo,ConnorGBrewster/servo,nnethercote/servo,CJ8664/servo,dsandeephegde/servo,KiChjang/servo,avadacatavra/servo,CJ8664/servo,rnestler/servo,fiji-flo/servo,emilio/servo,CJ8664/servo,eddyb/servo,larsbergstrom/servo,paulrouget/servo,saneyuki/servo,eddyb/servo,fiji-flo/servo,dsandeephegde/servo,szeged/servo,upsuper/servo,emilio/servo,paulrouget/servo,nnethercote/servo,sadmansk/servo,sadmansk/servo,cbrewster/servo,anthgur/servo,jimberlage/servo,CJ8664/servo,jimberlage/servo,larsbergstrom/servo,dsandeephegde/servo,canaltinova/servo,avadacatavra/servo,thiagopnts/servo,notriddle/servo,upsuper/servo,larsbergstrom/servo,DominoTree/servo,upsuper/servo,DominoTree/servo,KiChjang/servo,fiji-flo/servo,canaltinova/servo,mbrubeck/servo,thiagopnts/servo,mattnenterprise/servo,szeged/servo,paulrouget/servo,thiagopnts/servo,peterjoel/servo,splav/servo,rnestler/servo,KiChjang/servo,upsuper/servo,pyfisch/servo,nnethercote/servo,anthgur/servo,KiChjang/servo,DominoTree/servo,rnestler/servo,splav/servo,anthgur/servo,notriddle/servo,mattnenterprise/servo,CJ8664/servo,avadacatavra/servo,canaltinova/servo,KiChjang/servo,rnestler/servo,saneyuki/servo,SimonSapin/servo,SimonSapin/servo,pyfisch/servo,pyfisch/servo,cbrewster/servo,SimonSapin/servo,dati91/servo,canaltinova/servo,pyfisch/servo,eddyb/servo,eddyb/servo,jimberlage/servo,splav/servo,pyfisch/servo,avadacatavra/servo,fiji-flo/servo,mattnenterprise/servo,anthgur/servo,SimonSapin/servo,ConnorGBrewster/servo,KiChjang/servo,notriddle/servo,emilio/servo,emilio/servo,dsandeephegde/servo,sadmansk/servo,avadacatavra/servo,emilio/servo,eddyb/servo,jimberlage/servo,nnethercote/servo,fiji-flo/servo,saneyuki/servo,dati91/servo,DominoTree/servo,emilio/servo,larsbergstrom/servo,sadmansk/servo,dati91/servo,szeged/servo,mattnenterprise/servo,mbrubeck/servo,dsandeephegde/servo,emilio/servo,mbrubeck/servo,peterjoel/servo,paulrouget/servo,DominoTree/servo,thiagopnts/servo,splav/servo,CJ8664/servo,nnethercote/servo,canaltinova/servo,sadmansk/servo,paulrouget/servo,saneyuki/servo,cbrewster/servo,mattnenterprise/servo,ConnorGBrewster/servo,splav/servo,cbrewster/servo,ConnorGBrewster/servo,upsuper/servo,jimberlage/servo,dati91/servo,KiChjang/servo,peterjoel/servo,ConnorGBrewster/servo,cbrewster/servo,DominoTree/servo,avadacatavra/servo,KiChjang/servo,notriddle/servo,pyfisch/servo,mbrubeck/servo,cbrewster/servo,thiagopnts/servo,canaltinova/servo,KiChjang/servo,paulrouget/servo,peterjoel/servo,pyfisch/servo,thiagopnts/servo,jimberlage/servo,anthgur/servo,mbrubeck/servo,dsandeephegde/servo,saneyuki/servo,notriddle/servo,canaltinova/servo,SimonSapin/servo,larsbergstrom/servo,paulrouget/servo,splav/servo,szeged/servo,peterjoel/servo,SimonSapin/servo,fiji-flo/servo,nnethercote/servo,eddyb/servo,sadmansk/servo,dati91/servo,notriddle/servo,nnethercote/servo,ConnorGBrewster/servo,avadacatavra/servo,splav/servo,thiagopnts/servo,mattnenterprise/servo,upsuper/servo,emilio/servo,thiagopnts/servo,mattnenterprise/servo,mbrubeck/servo,rnestler/servo,peterjoel/servo,anthgur/servo,anthgur/servo,nnethercote/servo,szeged/servo,paulrouget/servo,jimberlage/servo,avadacatavra/servo,notriddle/servo,sadmansk/servo,SimonSapin/servo,anthgur/servo,eddyb/servo,saneyuki/servo,notriddle/servo,emilio/servo,dati91/servo,mattnenterprise/servo,saneyuki/servo,nnethercote/servo,rnestler/servo,cbrewster/servo,notriddle/servo,dsandeephegde/servo,pyfisch/servo,notriddle/servo,dati91/servo,nnethercote/servo,peterjoel/servo,SimonSapin/servo,mbrubeck/servo,saneyuki/servo,DominoTree/servo,dsandeephegde/servo,dati91/servo,DominoTree/servo,cbrewster/servo,CJ8664/servo,larsbergstrom/servo,splav/servo,paulrouget/servo,larsbergstrom/servo,DominoTree/servo,pyfisch/servo,upsuper/servo,mbrubeck/servo