Offer to regexp-quote new items in erc-match commands

Offer to regexp-quote new items in erc-match commands

* lisp/erc/erc-match.el (erc-match-quote-when-adding) Add new option
to quote new items added to match lists.
(erc-add-entry-to-list): Add optional `alt' parameter indicating
whether to flip the behavior indicated by
`erc-match-quote-when-adding'.
(erc-add-pal, erc-add-fool, erc-add-keyword, erc-add-dangerous-host):
Pass universal arg to `erc-add-entry-to-list' as `alt' argument.
(erc-match-pal-p, erc-match-fool-p, erc-match-keyword-p,
erc-match-dangerous-host-p): Don't bother matching when list is nil.

* lisp/erc/erc.el (erc-list-match (lst str): Join input list as regexp
union instead of looping over items.

* etc/ERC-NEWS: Update misc-UX section for 5.5.

* test/lisp/erc/erc-match-tests.el: New file. (Bug#56450)