Define class SelectionState; move some TrackPanel functions into it

src/SelectionState.h

@@ -0,0 +1,43 @@
+/**********************************************************************
+
+ Audacity: A Digital Audio Editor
+
+ SelectionState.h
+
+ **********************************************************************/
+
+#ifndef __AUDACITY_SELECTION_STATE__
+#define __AUDACITY_SELECTION_STATE__
+
+class Track;
+class TrackList;
+class MixerBoard;
+class ViewInfo;
+
+// State relating to the set of selected tracks
+class SelectionState
+{
+public:
+   static void SelectTrackLength
+      ( TrackList &tracks, ViewInfo &viewInfo, Track &track, bool syncLocked );
+
+   void SelectTrack
+      ( TrackList &tracks, Track &track,
+        bool selected, bool updateLastPicked, MixerBoard *pMixerBoard );
+   // Inclusive range of tracks, the limits specified in either order:
+   void SelectRangeOfTracks
+      ( TrackList &tracks, Track &sTrack, Track &eTrack,
+        MixerBoard *pMixerBoard );
+   void SelectNone( TrackList &tracks, MixerBoard *pMixerBoard );
+   void ChangeSelectionOnShiftClick
+      ( TrackList &tracks, Track &track, MixerBoard *pMixerBoard );
+   void HandleListSelection
+      ( TrackList &tracks, ViewInfo &viewInfo, Track &track,
+        bool shift, bool ctrl, bool syncLocked, MixerBoard *pMixerBoard );
+
+   void TrackListUpdated( const TrackList &tracks );
+
+   Track *mLastPickedTrack {};
+};
+
+#endif