Simplify by removing class HitTestResult...

... Because all hit tests returned all fields blank, or else, returned a
UIHandle object whose Preview method gives the rest of the information; so
the other fields were redundant.

src/WaveTrack.h

@@ -107,7 +107,7 @@ class AUDACITY_DLL_API WaveTrack final : public PlayableTrack {
 
    virtual ~WaveTrack();
 
-   HitTestResult DetailedHitTest
+   UIHandlePtr DetailedHitTest
       (const TrackPanelMouseState &state,
        const AudacityProject *pProject, int currentTool, bool bMultiTool)
       override;