maint: Updating naming conventions for exceptions and use const where possible. * GLCanvas.cc, interpreter-qobject.cc, file-editor-tab.cc, octave-qscintilla.cc, octave-qobject.cc, Cell.cc, __eigs__.cc, __magick_read__.cc, __qp__.cc, daspk.cc, dasrt.cc, dassl.cc, data.cc, file-io.cc, graphics.cc, graphics.in.h, input.cc, interpreter.cc, ls-mat-ascii.cc, lsode.cc, oct-handle.h, oct-map.cc, quad.cc, rand.cc, sparse.cc, sub2ind.cc, toplev.cc, utils.cc, __init_gnuplot__.cc, __ode15__.cc, cdef-object.cc, ov-base-diag.cc, ov-base-mat.cc, ov-base-sparse.cc, ov-base.cc, ov-fcn-handle.cc, ov-java.cc, ov-perm.cc, ov-range.cc, ov-re-diag.cc, ov-str-mat.cc, ov.cc, pt-assign.cc, pt-eval.cc, pt-idx.cc, pt-jit.cc, pt.cc, Array-util.cc, randmtzig.cc: Update naming conventions for exceptions to use initial letter of exception type. For example, "execution_exception" is named "ee", "index_exception" is "ie". Catch "const" exceptions where possible. * gzip.cc: Add block to catch and throw interrupt_exceptions before having a catch block "(...)" for everything else.

--- a/liboctave/array/Array-util.cc	Tue Dec 08 21:34:55 2020 +0100
+++ b/liboctave/array/Array-util.cc	Tue Dec 08 13:25:03 2020 -0800
@@ -561,13 +561,13 @@
           if (idx.extent (n) > n)
             octave::err_index_out_of_range (len, i+1, idx.extent (n), n, dv);
         }
-      catch (octave::index_exception& e)
+      catch (octave::index_exception& ie)
         {
-          e.set_pos_if_unset (len, i+1);
-          e.set_var ();
-          std::string msg = e.message ();
+          ie.set_pos_if_unset (len, i+1);
+          ie.set_var ();
+          std::string msg = ie.message ();
           (*current_liboctave_error_with_id_handler)
-            (e.err_id (), "%s", msg.c_str ());
+            (ie.err_id (), "%s", msg.c_str ());
         }
     }
   // idxa known to be valid.