SourceKit: use `std::chrono` in unittests
SourceKit: use `std::chrono` in unittests

Rather than using the `usleep` function which is both deprecated and
non-portable (does not exist on Windows), prefer using the C++11 chrono library
for the sleep.  This also allows us to use the UDL to simplify the code rather
than relying on the comments.  NFCI

aschwaighofer/swift,roambotics/swift,amraboelela/swift,airspeedswift/swift,xedin/swift,parkera/swift,xwu/swift,practicalswift/swift,amraboelela/swift,jmgc/swift,benlangmuir/swift,karwa/swift,shajrawi/swift,apple/swift,atrick/swift,airspeedswift/swift,shajrawi/swift,shahmishal/swift,shajrawi/swift,aschwaighofer/swift,gribozavr/swift,lorentey/swift,hooman/swift,ahoppen/swift,apple/swift,lorentey/swift,gregomni/swift,hooman/swift,benlangmuir/swift,jmgc/swift,stephentyrone/swift,sschiau/swift,parkera/swift,hooman/swift,jmgc/swift,airspeedswift/swift,JGiola/swift,tkremenek/swift,apple/swift,CodaFi/swift,harlanhaskins/swift,amraboelela/swift,atrick/swift,airspeedswift/swift,gregomni/swift,hooman/swift,shajrawi/swift,sschiau/swift,karwa/swift,jckarter/swift,CodaFi/swift,practicalswift/swift,xwu/swift,stephentyrone/swift,aschwaighofer/swift,practicalswift/swift,benlangmuir/swift,xedin/swift,allevato/swift,jmgc/swift,amraboelela/swift,gribozavr/swift,practicalswift/swift,karwa/swift,nathawes/swift,shahmishal/swift,harlanhaskins/swift,devincoughlin/swift,airspeedswift/swift,parkera/swift,parkera/swift,jmgc/swift,JGiola/swift,rudkx/swift,shahmishal/swift,benlangmuir/swift,lorentey/swift,karwa/swift,parkera/swift,devincoughlin/swift,harlanhaskins/swift,CodaFi/swift,rudkx/swift,shahmishal/swift,parkera/swift,parkera/swift,nathawes/swift,jckarter/swift,karwa/swift,roambotics/swift,allevato/swift,shahmishal/swift,roambotics/swift,aschwaighofer/swift,harlanhaskins/swift,sschiau/swift,glessard/swift,devincoughlin/swift,apple/swift,lorentey/swift,allevato/swift,ahoppen/swift,aschwaighofer/swift,stephentyrone/swift,ahoppen/swift,harlanhaskins/swift,apple/swift,devincoughlin/swift,aschwaighofer/swift,hooman/swift,xedin/swift,stephentyrone/swift,rudkx/swift,airspeedswift/swift,xedin/swift,xedin/swift,roambotics/swift,devincoughlin/swift,lorentey/swift,CodaFi/swift,JGiola/swift,lorentey/swift,tkremenek/swift,atrick/swift,roambotics/swift,JGiola/swift,practicalswift/swift,xwu/swift,devincoughlin/swift,lorentey/swift,shajrawi/swift,jckarter/swift,gribozavr/swift,gregomni/swift,xedin/swift,amraboelela/swift,tkremenek/swift,jmgc/swift,shajrawi/swift,tkremenek/swift,tkremenek/swift,allevato/swift,allevato/swift,atrick/swift,CodaFi/swift,stephentyrone/swift,devincoughlin/swift,shajrawi/swift,practicalswift/swift,nathawes/swift,rudkx/swift,shahmishal/swift,atrick/swift,xwu/swift,practicalswift/swift,sschiau/swift,karwa/swift,shajrawi/swift,roambotics/swift,jckarter/swift,atrick/swift,amraboelela/swift,allevato/swift,hooman/swift,tkremenek/swift,airspeedswift/swift,nathawes/swift,apple/swift,sschiau/swift,karwa/swift,gribozavr/swift,gregomni/swift,shahmishal/swift,JGiola/swift,jckarter/swift,hooman/swift,ahoppen/swift,ahoppen/swift,glessard/swift,lorentey/swift,amraboelela/swift,nathawes/swift,practicalswift/swift,nathawes/swift,jckarter/swift,jckarter/swift,karwa/swift,harlanhaskins/swift,gribozavr/swift,CodaFi/swift,xwu/swift,xedin/swift,gregomni/swift,JGiola/swift,sschiau/swift,tkremenek/swift,glessard/swift,glessard/swift,aschwaighofer/swift,allevato/swift,gribozavr/swift,rudkx/swift,glessard/swift,gregomni/swift,stephentyrone/swift,benlangmuir/swift,shahmishal/swift,xwu/swift,glessard/swift,gribozavr/swift,benlangmuir/swift,jmgc/swift,xwu/swift,harlanhaskins/swift,devincoughlin/swift,rudkx/swift,xedin/swift,stephentyrone/swift,sschiau/swift,nathawes/swift,gribozavr/swift,sschiau/swift,ahoppen/swift,CodaFi/swift,parkera/swift