Implement pinch zoom emulation to the glutin port
Implement pinch zoom emulation to the glutin port

The GLFW port had pinch zoom emulation that could be triggered by
holding control and using the mouse wheel. This was very useful for
testing pinch zoom behavior on desktop machines. This commit
implements this for the glutin port.

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