Preprocess prompt input linewise in ERC

Preprocess prompt input linewise in ERC

* etc/ERC-NEWS: Mention revised role of `erc-pre-send-functions'
relative to line splitting.
* lisp/erc/erc-common.el (erc-input): Add new slot `refoldp' to allow
`erc-pre-send-functions' members to indicate that splitting should
occur a second time after all members have had their say.
(erc--input-split): Specify some defaults for overridden slots and
explicitly declare some types for good measure.
* lisp/erc/erc-goodies.el (erc-noncommands-mode,
erc-noncommands-enable, erc-noncommands-disable): Replace
`erc-pre-send-functions' with `erc--input-review-functions'.
* lisp/erc/erc-ring.el (erc-ring-enable, erc-ring-disable,
erc-ring-mode): Subscribe to `erc--input-review-functions' instead of
`erc-pre-send-functions' for `erc--add-to-input-ring'.
* lisp/erc/erc.el (erc-pre-send-functions): Note some nuances
regarding line splitting in doc string and note that a new slot is
available.
(erc--pre-send-split-functions, erc--input-review-functions): Rename
former to latter, while also obsoleting.  Remove large comment.  Add
new default member `erc--run-input-validation-checks'.
(erc-send-modify-hook): Replace the obsolete `erc-send-pre-hook' and
`erc-send-this' with `erc-pre-send-functions' in doc string.
(erc--check-prompt-input-for-excess-lines): Don't trim trailing
blanks.  Rework to also report overages in characters as well as
lines.
(erc--run-input-validation-hooks): New function to adapt an
`erc--input-split' object to `erc--check-prompt-input-functions'.
(erc-send-current-line): Run `erc--input-review-functions' in place of
the validation hooks they've subsumed.  Call `erc--send-input-lines'
instead of the now retired but not deprecated `erc-send-input'.
(erc--run-send-hooks, erc--send-input-lines): New functions that
together form an alternate version of `erc-send-input'.  They operate
on input linewise but make accommodations for older interfaces.
* test/lisp/erc/erc-tests.el (erc-ring-previous-command): Replace
`erc-pre-send-functions' with `erc--input-review-functions'.
(erc-tests--with-process-input-spy): Shadow
`erc--input-review-functions'.
(erc-check-prompt-input-for-excess-lines): Don't expect trailing
blanks to be trimmed.
(erc--run-send-hooks): New test.  (Bug#62947)