delaunayn simplex check consistency and performance improvement (bug #60818) * delaunayn.m: Apply consistent volume calculation across all trivial simplex removal code paths. Vectorize 3D simplex removal code path and minimize function calls within >3D loop for performance improvement. Update FIXME note for future performance improvement. Add input type validation checks. Add BISTs for dimensions other than 2D, simplex removal, and input validation. * etc/News.8.md: Describe function improvements under General Improvements.

function [m_exist, n_exist] = ntest53027a ()
  global x
  x = 3;
  n_exist = nest ();
  m_exist = exist ("x", 'var');
  function n_exist = nest ()
    x = 1;
    clear x
    n_exist = exist ("x", "var");
  endfunction
endfunction