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/libinterp/octave-value/ov-fcn-handle.cc	Tue Dec 08 21:34:55 2020 +0100
+++ b/libinterp/octave-value/ov-fcn-handle.cc	Tue Dec 08 13:25:03 2020 -0800
@@ -837,7 +837,7 @@
 
                     arg_list.clear ();
                   }
-                catch (index_exception&)
+                catch (const index_exception&)
                   {
                     err_invalid_fcn_handle (m_name);
                   }