[utils] Minor Python tidies in utils/swift-bench.py (#4618)
[utils] Minor Python tidies in utils/swift-bench.py (#4618)

* [utils] Minor Python tidies in utils/swift-bench.py

* Track the line number where benchmarks are found
* Tidy up the argument parsing code for the default `--compiler` value
* Pull the regex for finding benchmarks out into a top-level constant,
  and add comments for improved readability

* Fix Python lint issue

devincoughlin/swift,frootloops/swift,jopamer/swift,tinysun212/swift-windows,glessard/swift,OscarSwanros/swift,brentdax/swift,return/swift,return/swift,sschiau/swift,swiftix/swift,jopamer/swift,JaSpa/swift,gmilos/swift,karwa/swift,lorentey/swift,tkremenek/swift,shahmishal/swift,tardieu/swift,kstaring/swift,djwbrown/swift,natecook1000/swift,stephentyrone/swift,hughbe/swift,parkera/swift,calebd/swift,allevato/swift,shajrawi/swift,airspeedswift/swift,amraboelela/swift,felix91gr/swift,CodaFi/swift,manavgabhawala/swift,tjw/swift,nathawes/swift,kperryua/swift,codestergit/swift,shahmishal/swift,calebd/swift,manavgabhawala/swift,tjw/swift,milseman/swift,kperryua/swift,alblue/swift,natecook1000/swift,djwbrown/swift,gmilos/swift,brentdax/swift,arvedviehweger/swift,arvedviehweger/swift,practicalswift/swift,milseman/swift,sschiau/swift,djwbrown/swift,tjw/swift,tardieu/swift,huonw/swift,parkera/swift,deyton/swift,hughbe/swift,harlanhaskins/swift,hooman/swift,glessard/swift,shahmishal/swift,jmgc/swift,bitjammer/swift,return/swift,parkera/swift,ahoppen/swift,devincoughlin/swift,deyton/swift,felix91gr/swift,alblue/swift,tkremenek/swift,swiftix/swift,modocache/swift,austinzheng/swift,allevato/swift,frootloops/swift,kperryua/swift,practicalswift/swift,deyton/swift,roambotics/swift,return/swift,felix91gr/swift,apple/swift,harlanhaskins/swift,harlanhaskins/swift,djwbrown/swift,ben-ng/swift,codestergit/swift,arvedviehweger/swift,felix91gr/swift,xedin/swift,JaSpa/swift,uasys/swift,shahmishal/swift,OscarSwanros/swift,practicalswift/swift,hooman/swift,calebd/swift,IngmarStein/swift,gmilos/swift,bitjammer/swift,xwu/swift,sschiau/swift,austinzheng/swift,gribozavr/swift,codestergit/swift,deyton/swift,gregomni/swift,lorentey/swift,parkera/swift,therealbnut/swift,austinzheng/swift,felix91gr/swift,practicalswift/swift,jtbandes/swift,hughbe/swift,sschiau/swift,OscarSwanros/swift,tinysun212/swift-windows,codestergit/swift,zisko/swift,apple/swift,tjw/swift,CodaFi/swift,atrick/swift,nathawes/swift,lorentey/swift,gribozavr/swift,deyton/swift,alblue/swift,Jnosh/swift,airspeedswift/swift,arvedviehweger/swift,huonw/swift,natecook1000/swift,benlangmuir/swift,ben-ng/swift,huonw/swift,austinzheng/swift,CodaFi/swift,glessard/swift,danielmartin/swift,ben-ng/swift,aschwaighofer/swift,ben-ng/swift,shajrawi/swift,uasys/swift,swiftix/swift,shahmishal/swift,tjw/swift,huonw/swift,therealbnut/swift,danielmartin/swift,manavgabhawala/swift,gribozavr/swift,harlanhaskins/swift,brentdax/swift,devincoughlin/swift,xedin/swift,JaSpa/swift,ahoppen/swift,jmgc/swift,tkremenek/swift,benlangmuir/swift,JaSpa/swift,roambotics/swift,gregomni/swift,CodaFi/swift,therealbnut/swift,ahoppen/swift,hooman/swift,bitjammer/swift,stephentyrone/swift,deyton/swift,brentdax/swift,benlangmuir/swift,CodaFi/swift,brentdax/swift,benlangmuir/swift,zisko/swift,IngmarStein/swift,JGiola/swift,jopamer/swift,Jnosh/swift,roambotics/swift,stephentyrone/swift,gmilos/swift,brentdax/swift,tinysun212/swift-windows,devincoughlin/swift,amraboelela/swift,huonw/swift,frootloops/swift,natecook1000/swift,allevato/swift,benlangmuir/swift,gottesmm/swift,jopamer/swift,deyton/swift,jckarter/swift,uasys/swift,hooman/swift,zisko/swift,gmilos/swift,xwu/swift,swiftix/swift,ahoppen/swift,djwbrown/swift,jtbandes/swift,aschwaighofer/swift,modocache/swift,jmgc/swift,manavgabhawala/swift,calebd/swift,hughbe/swift,swiftix/swift,calebd/swift,sschiau/swift,aschwaighofer/swift,amraboelela/swift,calebd/swift,glessard/swift,glessard/swift,sschiau/swift,jckarter/swift,kperryua/swift,parkera/swift,felix91gr/swift,zisko/swift,gottesmm/swift,stephentyrone/swift,apple/swift,hooman/swift,tkremenek/swift,gribozavr/swift,modocache/swift,harlanhaskins/swift,ben-ng/swift,natecook1000/swift,lorentey/swift,shahmishal/swift,amraboelela/swift,roambotics/swift,jtbandes/swift,practicalswift/swift,airspeedswift/swift,arvedviehweger/swift,JGiola/swift,aschwaighofer/swift,calebd/swift,tjw/swift,jmgc/swift,jopamer/swift,jtbandes/swift,zisko/swift,parkera/swift,allevato/swift,tinysun212/swift-windows,danielmartin/swift,JaSpa/swift,milseman/swift,xwu/swift,harlanhaskins/swift,return/swift,rudkx/swift,huonw/swift,jckarter/swift,xwu/swift,xedin/swift,devincoughlin/swift,swiftix/swift,amraboelela/swift,jopamer/swift,jmgc/swift,allevato/swift,karwa/swift,alblue/swift,tardieu/swift,gottesmm/swift,therealbnut/swift,atrick/swift,jopamer/swift,xwu/swift,tinysun212/swift-windows,tjw/swift,aschwaighofer/swift,JaSpa/swift,atrick/swift,codestergit/swift,karwa/swift,hughbe/swift,ben-ng/swift,OscarSwanros/swift,atrick/swift,danielmartin/swift,alblue/swift,allevato/swift,CodaFi/swift,jmgc/swift,milseman/swift,alblue/swift,JGiola/swift,apple/swift,arvedviehweger/swift,JGiola/swift,rudkx/swift,nathawes/swift,uasys/swift,return/swift,lorentey/swift,bitjammer/swift,shahmishal/swift,xedin/swift,shajrawi/swift,shajrawi/swift,rudkx/swift,aschwaighofer/swift,djwbrown/swift,roambotics/swift,austinzheng/swift,Jnosh/swift,nathawes/swift,kstaring/swift,xedin/swift,zisko/swi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