Improve ERC's matching of nicks and URLs (bug#38257)

Improve ERC's matching of nicks and URLs (bug#38257)

* lisp/erc/erc-{button,match}.el (erc-{button,match}-syntax-table):
Omit (, ), and '; as they're not valid nick characters, per RFC 2812
section 2.3.1.  This enables correct matching/highlighting of nicks
when they're surrounded by parens, like (nick), and when adjacent to
an apostrophe, like nick's.
* lisp/erc/erc-button.el (erc-button-url-regexp): Use the regexp from
browse-url-button-regexp, which among other things, seems to handle
surrounding pair of parens better.