Don't nest date stamp insertions in erc-stamp

Don't nest date stamp insertions in erc-stamp

* etc/ERC-NEWS: Don't mention certain insertion-adjacent hooks being
suppressed for date stamps, which is no longer true.
* lisp/erc/erc-common.el (erc--solo): New utility function.
* lisp/erc/erc-fill.el (erc-fill-wrap): Don't move last-message marker
when encountering a date stamp.
* lisp/erc/erc-stamp.el (erc-stamp--recover-on-reconnect): Restore
`erc-stamp--date-stamps' on reconnect and rejoin.
(erc-stamp--insert-date-hook): Fix erroneous doc string.
(erc-stamp--date): New struct type.
(erc-stamp--deferred-date-stamp): New internal variable to pass state
between hook members.
(erc-stamp--date-stamps): New internal variable to store a reference
to all inserted timestamps.
(erc-stamp--propertize-left-date-stamp): Don't hide messages because
this function runs on `erc-insert-modify-hook'.  Prefer doing so
later, in `erc-insert-post-hook'.
(erc-stamp--find-insertion-point): New helper function.
(erc-stamp--insert-date-stamp-as-phony-message): Remove.
(erc-stamp--lr-date-on-pre-modify): Remove function.  Portions of body
now appear in `erc-stamp--defer-date-insertion-on-post-modify'.
(erc-stamp--defer-date-insertion-on-post-modify)
(erc-stamp--defer-date-insertion-on-post-insert)
(erc-stamp--defer-date-insertion-on-post-send): New functions,
although the first incorporates parts of the now defunct
`erc-stamp--lr-date-on-pre-modify'.
(erc-stamp--date-mode): Update hook-member functions.
(erc-stamp-prepend-date-stamps-p): Revise doc.
(erc-insert-timestamp-left-and-right): Remove code to initialize a
date stamp in place through a nested call to `erc-display-message'.
Instead, "pre-render" date stamp and stash it for retrieval by
the function `erc-stamp--defer-date-insertion-on-post-modify'.
(erc-stamp--setup): Kill variables `erc-stamp--deferred-date-stamp'
and `erc-stamp--date-stamps'.
(erc-stamp--reset-on-clear): Remove trimmed stamps from
`erc-stamp--date-stamps'.
* lisp/erc/erc.el (erc--msg-props): Document `erc--hide' in doc
string.
(erc--with-inserted-msg): Remove unused macro.
(erc--insert-line-splice-function): New variable.
(erc--with-spliced-insertion): New macro.
(erc--insert-line-function): Expand doc string.
(erc--remove-from-prop-value-list): Tweak doc string.
(erc--insert-before-markers-transplanting-hidden): New function.
(erc--hide-message): Remember managed `invisible' prop value.  Do so
by recording them in the `erc--hide' "msg prop".
(erc--delete-inserted-message, erc--delete-inserted-message-naively):
Rename former to latter to emphasize that it's largely impractical for
general use.
(erc--ranked-properties): Add `erc--hide'.
* test/lisp/erc/erc-button-tests.el
(erc-button-tests--erc-button-alist--function-as-form): Use
`erc-display-message' helper.
* test/lisp/erc/erc-fill-tests.el (erc-fill-tests--insert-privmsg)
(erc-fill-tests--wrap-populate, erc-fill-wrap-tests--merge-action)
(erc-fill-line-spacing): Use `erc-display-message' wrappers to
intercept `erc-timer-hook' modifications.
* test/lisp/erc/erc-scenarios-match.el
(erc-scenarios-match--invisible-stamp): Add convenience commands to
`extended-command-history' when running interactively.
* test/lisp/erc/erc-tests.el
(erc--insert-before-markers-transplanting-hidden): New test.
(erc--delete-inserted-message, erc--delete-inserted-message-naively):
Update test name as well as namesake function in body.
* test/lisp/erc/resources/erc-scenarios-common.el
(erc-scenarios-common-with-cleanup): Validate `erc-stamp--date-stamps'
members after every scenario test.
(erc-scenarios-common--assert-date-stamps): New function.
* test/lisp/erc/resources/erc-tests-common.el: Require `erc-stamp'
atop file when compiling.
(erc-tests--common-display-message)
(erc-tests-common-display-message)
(erc-tests-common-with-date-aware-display-message): New functions and
macro for running `erc-display-message' while intercepting additions
to `erc-timer-hook' made by date-stamp-related post-insertion hooks.
(erc-tests-common-snapshot-compare): Insert expected output into its
own buffer for easier review during interactive sessions.  This change
is unrelated to the rest of this commit.  (Bug#60936)

(cherry picked from commit 86184cba2180a09b31e92f7366f9dd38de5b976a)