add switching to previous workspace

src/helpers/Workspace.hpp

@@ -18,6 +18,9 @@ public:
     int             m_iID = -1;
     std::string     m_szName = "";
     uint64_t        m_iMonitorID = -1;
+    // Previous workspace ID is stored during a workspace change, allowing travel
+    // to the previous workspace.
+    int m_iPrevWorkspaceID = -1;
     bool            m_bHasFullscreenWindow = false;
     eFullscreenMode m_efFullscreenMode = FULLSCREEN_FULL;