doc: Update documentation for functions returning a graphics handle h (Bug #34761) * voronoi.m, image.m, imagesc.m, imshow.m, area.m, bar.m, barh.m, clabel.m, clf.m, compass.m, ezcontour.m, ezcontourf.m, ezmesh.m, ezmeshc.m, ezplot.m, ezplot3.m, ezpolar.m, ezsurf.m, ezsurfc.m, feather.m, fill.m, findall.m, findobj.m, loglog.m, mesh.m, pareto.m, patch.m, pie.m, pie3.m, plot.m, polar.m, quiver.m, quiver3.m, rectangle.m, ribbon.m, rose.m, scatter.m, scatter3.m, semilogx.m, semilogy.m, slice.m, stem.m, surf.m, surface.m, text.m, title.m, trimesh.m, triplot.m, trisurf.m, xlabel.m, ylabel.m, zlabel.m: Update documentation for functions returning a graphics handle h.

--- a/scripts/plot/plot.m
+++ b/scripts/plot/plot.m
@@ -173,6 +173,8 @@
 ## If the first argument is an axis handle, then plot into these axes,
 ## rather than the current axis handle returned by @code{gca}.
 ##
+## The optional return value @var{h} is a graphics handle to the created plot.
+##
 ## @seealso{semilogx, semilogy, loglog, polar, mesh, contour, bar,
 ## stairs, errorbar, xlabel, ylabel, title, print}
 ## @end deftypefn
@@ -201,3 +203,7 @@
   endif
 
 endfunction
+
+
+%% FIXME: Need demo or test for function
+