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:

> I've added these changes as
>
>   https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=c68dc778
>
> Although I've done so with zero discussion, as usual, others can perhaps
> take some comfort in knowing that this semi-major overhaul only reaches
> as far back as the latest release (but not into it). Thanks.

These changes introduced a(t least one) bug. To reproduce, call
`erc-display-line' with a list of buffers, and notice only the first
sees its message inserted with the correct text properties. A quick way
to simulate this is by having two clients join the same two channels
and then having one quit. The expected text props will be missing from
one of the inserted

  *** someuser (n!~u@h) has quit

messages. Verify by going to the first asterisk and doing C-u C-x =.

Fix forthcoming.