Revive erc-command-indicator as new module

* doc/misc/erc.texi: Add entry for `command-indicator' to Modules
chapter.
* etc/ERC-NEWS: Mention new module `command-indicator'.
* lisp/erc/erc-goodies.el (erc-noncommands-list): Replace the
nonexistent `erc-cmd-SMV' with function `erc-cmd-SAY'.
(erc-noncommands-mode, erc-noncommands-enable,
erc-noncommands-disable): Deprecate this module because it's a no-op.
(erc-command-indicator-face, erc-command-indicator): Migrate from main
library.
(erc-command-indicator-mode, erc-command-indicator-enable,
erc-command-indicator-disable): New module to take the spiritual place
of `noncommands'.
(erc-command-indicator): Move function here from main library, along
with option namesake mentioned above.
(erc-command-indicator-toggle-hidden): New command to toggle echoed
command-line visibility.
(erc--command-indicator-permit-insertion): New function.
(erc--command-indicator-display): New function, a slightly revised
version of the old `erc-display-command' from the main library.  Its
only call site was removed back in d1036d288d "backport: erc
bugfixes".  However, references were left behind to associated assets,
like `erc-command-indicator', etc.  The function was later commented
out in 0c599ee2e2 "* lisp/erc/erc.el: Use `run-hook-with-args` for
`erc-pre-send-functions`", and then removed by a63ed6f78a "Remove
duplicate ERC prompt on reconnect".
* lisp/erc/erc-match.el (erc-match-toggle-hidden-fools): Use new
non-module-specific name for `erc-match--toggle-hidden'.
(erc-match--toggle-hidden): Move to main library for shared use by
other modules.
* lisp/erc/erc.el (erc-hide-prompt): Leave note explaining updated
role.
(erc-command-indicator): Move option and function of same name to
erc-goodies.
(erc-command-indicator-face): Move to erc-goodies.
(erc-modules): Remove module `noncommands' from standard value and
Custom set.  Add `command-indicator' to set.
(erc--toggle-hidden): "New" function, a rebranded version of the
utility `erc-match--toggle-hidden' from erc-match.
(erc--send-input-lines): Accommodate modules wanting alternate
insertion functions.
(erc-load-irc-script-lines): Account for `erc-command-indicator' no
longer being defined in this library.
* test/lisp/erc/erc-scenarios-base-send-message.el
(erc-scenarios-base-send-message--command-indicator): New test.
* test/lisp/erc/erc-tests.el (erc-tests--modules): Remove
deprecated module `noncommands' from manifest.  (Bug#67031)

test/lisp/erc/erc-tests.el

@@ -2543,7 +2543,8 @@
     (kill-buffer "#chan")))
 
 (defconst erc-tests--modules
-  '( autoaway autojoin bufbar button capab-identify completion dcc fill identd
+  '( autoaway autojoin bufbar button capab-identify
+     command-indicator completion dcc fill identd
      imenu irccontrols keep-place list log match menu move-to-prompt netsplit
      networks nickbar nicks noncommands notifications notify page readonly
      replace ring sasl scrolltobottom services smiley sound