Add wxGrid::GetSelectedRowBlocks() and GetSelectedColBlocks()

These functions are much simpler to use in the application code using
wxGrid in row- or column-only selection mode than GetSelectedBlocks()
itself because they take care of deduplicating, ordering and squashing
together the adjacent ranges, so that the application can use their
results directly, unlike with GetSelectedBlocks().

interface/wx/grid.h

@@ -4675,10 +4675,50 @@ public:
             }
         @endcode
 
+        Notice that the blocks returned by this method are not ordered in any
+        particular way and may overlap. For grids using rows or columns-only
+        selection modes, GetSelectedRowBlocks() or GetSelectedColBlocks() can
+        be more convenient, as they return ordered and non-overlapping blocks.
+
         @since 3.1.4
     */
     wxGridBlocks GetSelectedBlocks() const;
 
+    /**
+        Returns an ordered range of non-overlapping selected rows.
+
+        For the grids using wxGridSelectRows selection mode, returns the
+        possibly empty vector containing the coordinates of non-overlapping
+        selected row blocks in the natural order, i.e. from smallest to the
+        biggest row indices.
+
+        To see the difference between this method and GetSelectedBlocks(),
+        consider the case when the user selects rows 2..4 in the grid and then
+        also selects (using Ctrl/Shift keys) the rows 1..3. Iterating over the
+        result of GetSelectedBlocks() would yield two blocks directly
+        corresponding to the users selection, while this method returns a
+        vector with a single element corresponding to the rows 1..4.
+
+        This method returns empty vector for the other selection modes.
+
+        @see GetSelectedBlocks(), GetSelectedColBlocks()
+
+        @since 3.1.4
+     */
+    wxGridBlockCoordsVector GetSelectedRowBlocks() const;
+
+    /**
+        Returns an ordered range of non-overlapping selected columns.
+
+        This method is symmetric to GetSelectedRowBlocks(), but is useful only
+        in wxGridSelectColumns selection mode.
+
+        @see GetSelectedBlocks()
+
+        @since 3.1.4
+     */
+    wxGridBlockCoordsVector GetSelectedColBlocks() const;
+
     /**
         Returns an array of individually selected cells.