Expose --histreedit and --histverify options (re: 921bbcae)

This adds two long-form shell options that modify history expansion
(-H/--histexpand). If --histreedit is on and a history expansion
fails, the command line is reloaded into the next prompt's edit
buffer, allowing corrections. If --histverify is on, the results of
a history expansion are not immediately executed but instead loaded
into the next prompt's edit buffer, allowing further changes.

SH_HISTREEDIT and SH_HISTVERIFY were already handled all along in
slowread() in io.c and via 'reedit' arguments to functions called
there, but could not be turned on as they were only ever exposed as
shopt options in the removed bash compatibility mode (in theory
only, as it failed to compile). I had overlooked them until now.

So, since the code is there, let's expose these options through the
normal long options interface. They're working fine, and activating
them actually makes history expansion tolerable to use.

src/cmd/ksh93/data/options.c:
- Make these options available as "histreedit" and "histverify".

src/cmd/ksh93/data/builtins.c,
src/cmd/ksh93/sh.1:
- Document the "new" options.

src/cmd/ksh93/include/defs.h:
- Remove unused SH_HISTAPPEND and SH_HISTORY2 macros which were
  part of the removed bash compatibility code. Note that ksh does
  not need a histappend option as it never overwrites the history
  file (in the bash mode, this shopt option was a no-op).

src/cmd/ksh93/include/defs.h

@@ -2,7 +2,7 @@
 *                                                                      *
 *               This software is part of the ast package               *
 *          Copyright (c) 1982-2012 AT&T Intellectual Property          *
-*          Copyright (c) 2020-2021 Contributors to ksh 93u+m           *
+*          Copyright (c) 2020-2022 Contributors to ksh 93u+m           *
 *                      and is licensed under the                       *
 *                 Eclipse Public License, Version 1.0                  *
 *                    by AT&T Intellectual Property                     *
@@ -104,9 +104,7 @@ extern char*	sh_setenviron(const char*);
 #define SH_TYPE_RESTRICTED	040
 
 #if SHOPT_HISTEXPAND
-#   define SH_HISTAPPEND	60
 #   define SH_HISTEXPAND	43
-#   define SH_HISTORY2		44
 #   define SH_HISTREEDIT	61
 #   define SH_HISTVERIFY	62
 #endif