[sil] Add an implicit operator bool conversion to SILDebugLocation.
[sil] Add an implicit operator bool conversion to SILDebugLocation.

The reason to do this is that one can now do:

```
if (auto debugLoc = i.getDebugLocation()) {
  // do something with debug loc.
}
```

I also cleaned up the style a little bit by renaming the internal ivars to be
camelCase.

gregomni/swift,rudkx/swift,jckarter/swift,airspeedswift/swift,atrick/swift,tkremenek/swift,apple/swift,CodaFi/swift,CodaFi/swift,jmgc/swift,roambotics/swift,jmgc/swift,xwu/swift,allevato/swift,tkremenek/swift,nathawes/swift,parkera/swift,parkera/swift,tkremenek/swift,allevato/swift,CodaFi/swift,glessard/swift,benlangmuir/swift,atrick/swift,JGiola/swift,roambotics/swift,jckarter/swift,airspeedswift/swift,jmgc/swift,roambotics/swift,hooman/swift,airspeedswift/swift,glessard/swift,allevato/swift,nathawes/swift,xwu/swift,CodaFi/swift,allevato/swift,nathawes/swift,ahoppen/swift,allevato/swift,ahoppen/swift,tkremenek/swift,roambotics/swift,parkera/swift,parkera/swift,allevato/swift,parkera/swift,benlangmuir/swift,nathawes/swift,rudkx/swift,apple/swift,benlangmuir/swift,CodaFi/swift,nathawes/swift,gregomni/swift,jckarter/swift,airspeedswift/swift,benlangmuir/swift,CodaFi/swift,airspeedswift/swift,rudkx/swift,atrick/swift,tkremenek/swift,jckarter/swift,airspeedswift/swift,JGiola/swift,parkera/swift,ahoppen/swift,rudkx/swift,glessard/swift,apple/swift,JGiola/swift,allevato/swift,atrick/swift,hooman/swift,xwu/swift,benlangmuir/swift,hooman/swift,gregomni/swift,nathawes/swift,jckarter/swift,parkera/swift,atrick/swift,apple/swift,ahoppen/swift,xwu/swift,JGiola/swift,rudkx/swift,gregomni/swift,xwu/swift,atrick/swift,airspeedswift/swift,jmgc/swift,gregomni/swift,glessard/swift,hooman/swift,glessard/swift,jckarter/swift,jmgc/swift,hooman/swift,roambotics/swift,nathawes/swift,hooman/swift,CodaFi/swift,tkremenek/swift,parkera/swift,JGiola/swift,ahoppen/swift,gregomni/swift,xwu/swift,apple/swift,jmgc/swift,tkremenek/swift,jmgc/swift,glessard/swift,apple/swift,jckarter/swift,roambotics/swift,ahoppen/swift,benlangmuir/swift,hooman/swift,xwu/swift,JGiola/swift,rudkx/swift