bug#60936: 30.0.50; ERC >5.5: Add erc-fill style based on visual-line-mode

[J.P.]

"J.P." <jp@neverwas.me> writes:

> Recent work on this feature introduced an annoying regression.
>
>>From emacs -Q:
>
>   1. M-: (erc-tls :server "testnet.inspircd.org") RET
>   2. /JOIN #test and say something
>   3. M-: (setq erc-timestamp-last-inserted-left nil) RET to reset the
>      date stamp's deduping snapshot
>   4. Say something else
>   5. Notice that point has been dislodged from the prompt and that a new
>      date stamp has not been inserted
>
> The second of the attached patches should fix it.

This and related fixes involving date stamps were recently installed.
See:

  * f99a0dae7ca Align date stamps to whole days in ERC
  * 4c851085769 Decouple disparate escape-hatch concerns in erc-stamp
  * 781f950edab Preserve user markers when inserting ERC date stamps
  * f7c7f7ac20d Don't over-truncate erc-timestamp-format-left

The second one might be of interest to users with a legitimate need to
call `erc-insert-line' (formerly `erc-display-line') directly, as
opposed to via `erc-display-message'. It's now possible to do so without
sacrificing timestamps and without also incurring the likely unwanted
`cursor-sensor-functions' property. (The latter now has its own separate
compatibility flag.)