Make wxGridEvent methods GetRow() and GetCol() const and not virtual

See #19085

docs/changes.txt

@@ -181,6 +181,8 @@ Changes in behaviour which may result in build errors
 - wxAuiMDIChildFrame now inherits from wxFrame and not wxPanel, you will need
   to change your code and XRC definitions accordingly.
 
+- wxGridEvent methods GetRow() and GetCol() are no longer virtual.
+
 
 3.1.5: (released 2020-10-??)
 ----------------------------

include/wx/generic/grid.h

@@ -3209,8 +3209,8 @@ public:
                 bool control,
                 bool shift = false, bool alt = false, bool meta = false));
 
-    virtual int GetRow() { return m_row; }
-    virtual int GetCol() { return m_col; }
+    int GetRow() const { return m_row; }
+    int GetCol() const { return m_col; }
     wxPoint GetPosition() const { return wxPoint( m_x, m_y ); }
     bool Selecting() const { return m_selecting; }
 

interface/wx/grid.h

@@ -6234,7 +6234,7 @@ public:
         column of the newly selected cell while the previously selected cell
         can be retrieved using wxGrid::GetGridCursorCol().
     */
-    virtual int GetCol();
+    int GetCol() const;
 
     /**
         Position in pixels at which the event occurred.
@@ -6248,7 +6248,7 @@ public:
         of the newly selected cell while the previously selected cell can be
         retrieved using wxGrid::GetGridCursorRow().
     */
-    virtual int GetRow();
+    int GetRow() const;
 
     /**
         Returns @true if the Meta key was down at the time of the event.