Auto merge of #20192 - servo:derive-all-the-things, r=emilio
Auto merge of #20192 - servo:derive-all-the-things, r=emilio

 Derive ToCss for DeclaredValue

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DominoTree/servo,anthgur/servo,avadacatavra/servo,jimberlage/servo,szeged/servo,larsbergstrom/servo,emilio/servo,paulrouget/servo,nnethercote/servo,mattnenterprise/servo,SimonSapin/servo,ConnorGBrewster/servo,KiChjang/servo,szeged/servo,dati91/servo,larsbergstrom/servo,pyfisch/servo,cbrewster/servo,canaltinova/servo,jimberlage/servo,emilio/servo,peterjoel/servo,notriddle/servo,cbrewster/servo,nnethercote/servo,anthgur/servo,nnethercote/servo,szeged/servo,saneyuki/servo,peterjoel/servo,emilio/servo,jimberlage/servo,paulrouget/servo,dati91/servo,emilio/servo,anthgur/servo,pyfisch/servo,mattnenterprise/servo,larsbergstrom/servo,nnethercote/servo,jimberlage/servo,pyfisch/servo,pyfisch/servo,KiChjang/servo,KiChjang/servo,KiChjang/servo,sadmansk/servo,splav/servo,szeged/servo,SimonSapin/servo,peterjoel/servo,saneyuki/servo,pyfisch/servo,szeged/servo,dati91/servo,SimonSapin/servo,szeged/servo,KiChjang/servo,mbrubeck/servo,pyfisch/servo,notriddle/servo,nnethercote/servo,emilio/servo,avadacatavra/servo,upsuper/servo,szeged/servo,sadmansk/servo,anthgur/servo,szeged/servo,paulrouget/servo,paulrouget/servo,pyfisch/servo,avadacatavra/servo,larsbergstrom/servo,KiChjang/servo,canaltinova/servo,mattnenterprise/servo,ConnorGBrewster/servo,emilio/servo,saneyuki/servo,KiChjang/servo,splav/servo,DominoTree/servo,saneyuki/servo,DominoTree/servo,splav/servo,canaltinova/servo,paulrouget/servo,dati91/servo,mbrubeck/servo,notriddle/servo,jimberlage/servo,DominoTree/servo,avadacatavra/servo,upsuper/servo,notriddle/servo,mbrubeck/servo,notriddle/servo,larsbergstrom/servo,avadacatavra/servo,avadacatavra/servo,ConnorGBrewster/servo,larsbergstrom/servo,jimberlage/servo,saneyuki/servo,upsuper/servo,szeged/servo,paulrouget/servo,ConnorGBrewster/servo,cbrewster/servo,saneyuki/servo,dati91/servo,splav/servo,larsbergstrom/servo,sadmansk/servo,peterjoel/servo,upsuper/servo,cbrewster/servo,anthgur/servo,splav/servo,KiChjang/servo,canaltinova/servo,mattnenterprise/servo,notriddle/servo,KiChjang/servo,DominoTree/servo,cbrewster/servo,splav/servo,sadmansk/servo,mbrubeck/servo,splav/servo,cbrewster/servo,upsuper/servo,KiChjang/servo,anthgur/servo,jimberlage/servo,mattnenterprise/servo,canaltinova/servo,notriddle/servo,emilio/servo,larsbergstrom/servo,saneyuki/servo,pyfisch/servo,larsbergstrom/servo,paulrouget/servo,paulrouget/servo,upsuper/servo,mattnenterprise/servo,upsuper/servo,jimberlage/servo,SimonSapin/servo,SimonSapin/servo,pyfisch/servo,jimberlage/servo,saneyuki/servo,pyfisch/servo,larsbergstrom/servo,upsuper/servo,mattnenterprise/servo,ConnorGBrewster/servo,mbrubeck/servo,mbrubeck/servo,saneyuki/servo,DominoTree/servo,avadacatavra/servo,notriddle/servo,peterjoel/servo,dati91/servo,ConnorGBrewster/servo,nnethercote/servo,peterjoel/servo,emilio/servo,splav/servo,DominoTree/servo,sadmansk/servo,DominoTree/servo,cbrewster/servo,canaltinova/servo,nnethercote/servo,canaltinova/servo,nnethercote/servo,splav/servo,ConnorGBrewster/servo,sadmansk/servo,SimonSapin/servo,peterjoel/servo,nnethercote/servo,ConnorGBrewster/servo,paulrouget/servo,sadmansk/servo,DominoTree/servo,szeged/servo,notriddle/servo,SimonSapin/servo,anthgur/servo,peterjoel/servo,splav/servo,DominoTree/servo,avadacatavra/servo,canaltinova/servo,cbrewster/servo,peterjoel/servo,mbrubeck/servo,dati91/servo,nnethercote/servo,emilio/servo,mbrubeck/servo,notriddle/servo,saneyuki/servo,SimonSapin/servo,dati91/servo,paulrouget/servo,peterjoel/servo,mattnenterprise/servo,emilio/servo,sadmansk/servo,anthgur/servo