Auto merge of #12821 - UK992:mach-update, r=aneeshusa
Auto merge of #12821 - UK992:mach-update, r=aneeshusa

Create `mach fetch` command

- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12775.

r? @larsbergstrom

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