doc: Use @code{} within alternate text for @xref,@pxref macros for better Info display. * accumarray.m, structfun.m, slash.m, csvread.m, csvwrite.m, edit.m, setfield.m, lsqnonneg.m, pqpnonneg.m, camlookat.m, camorbit.m, camup.m, barh.m, camlight.m, isocaps.m, isosurface.m, loglogerr.m, polar.m, reducepatch.m, reducevolume.m, semilogxerr.m, semilogyerr.m, findall.m, findobj.m, beta.m, movmad.m, movmax.m, movmean.m, movmedian.m, movmin.m, movprod.m, movstd.m, movsum.m, movvar.m, test.m, datenum.m: Place alternate text in @code{} macro so it displays better in plaintext Info.

--- a/scripts/statistics/movmad.m	Mon Oct 19 09:13:53 2020 -0700
+++ b/scripts/statistics/movmad.m	Mon Oct 19 09:33:28 2020 -0700
@@ -123,7 +123,7 @@
 ## @end table
 ##
 ## Programming Note: This function is a wrapper which calls @code{movfun}.
-## For additional options and documentation, @pxref{XREFmovfun,,movfun}.
+## For additional options and documentation, @pxref{XREFmovfun,,@code{movfun}}.
 ##
 ## @seealso{movfun, movslice, movmax, movmean, movmedian, movmin, movprod, movstd, movsum, movvar}
 ## @end deftypefn