maint: Use "fcn" as preferred abbreviation for "function" in libinterp/. * __eigs__.cc, bsxfun.cc, cellfun.cc, daspk.cc, dasrt.cc, dassl.cc, data.cc, debug.cc, error.cc, graphics.cc, graphics.in.h, gzfstream.h, ls-hdf5.cc, lsode.cc, max.cc, oct-opengl.h, quad.cc, strfns.cc, utils.cc, utils.h, variables.cc, __ode15__.cc, gzip.cc, cdef-manager.cc, ov-fcn-handle.cc, ov-java.cc, ov-usr-fcn.cc, bp-table.cc, bp-table.h, lex.h, lex.ll, oct-parse.yy, pt-eval.cc: Replace "func", "fun", "fn" in documentation and variable names with "fcn".

--- a/libinterp/corefcn/error.cc	Tue Apr 05 01:06:00 2022 -0400
+++ b/libinterp/corefcn/error.cc	Tue Apr 05 08:33:58 2022 -0700
@@ -125,10 +125,10 @@
   va_end (args);
 }
 
-typedef void (*error_fun)(const char *, const char *, ...);
+typedef void (*error_fcn)(const char *, const char *, ...);
 
 static std::string
-handle_message (error_fun f, const char *id, const char *msg,
+handle_message (error_fcn f, const char *id, const char *msg,
                 const octave_value_list& args, bool have_fmt)
 {
   std::string retval;