[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.

Author: gottesmm

include/swift/SIL/SILLocation.h

@@ -755,17 +755,18 @@ class SILDebugScope;
 
 /// A SILLocation paired with a SILDebugScope.
 class SILDebugLocation {
-  const SILDebugScope *Scope = nullptr;
-  SILLocation Location;
+  const SILDebugScope *debugScope;
+  SILLocation location;
 
 public:
   SILDebugLocation()
-      : Scope(nullptr),
-        Location(RegularLocation::getAutoGeneratedLocation()) {}
-  SILDebugLocation(SILLocation Loc, const SILDebugScope *DS)
-      : Scope(DS), Location(Loc) {}
-  SILLocation getLocation() const { return Location; }
-  const SILDebugScope *getScope() const { return Scope; }
+      : debugScope(nullptr),
+        location(RegularLocation::getAutoGeneratedLocation()) {}
+  SILDebugLocation(SILLocation location, const SILDebugScope *debugScope)
+      : debugScope(debugScope), location(location) {}
+  SILLocation getLocation() const { return location; }
+  const SILDebugScope *getScope() const { return debugScope; }
+  operator bool() const { return bool(location) && debugScope; }
 };
 
 } // end swift namespace