Add baseline test coverage for erc-match

Add baseline test coverage for erc-match

* lisp/erc/erc-match.el (erc-pal-highlight-type)
(erc-fool-highlight-type, erc-dangerous-host-highlight-type): Clarify
some areas in doc strings.
* test/lisp/erc/erc-match-tests.el: Require `erc-test-common' library.
(erc-match-tests--assert-face-absent)
(erc-match-tests--assert-face-present)
(erc-match-tests--assert-speaker-highlighted)
(erc-match-tests--assert-speaker-only-highlighted)
(erc-match-tests--perform)
(erc-match-tests--hl-type-nick): New functions.
(erc-match-message/pal/nick, erc-match-message/fool/nick)
(erc-match-message/dangerous-host/nick): New tests.
(erc-match-tests--hl-type-message): New function.
(erc-match-message/pal/message)
(erc-match-message/fool/message)
(erc-match-message/dangerous-host/message): New tests.
(erc-match-tests--hl-type-all): New function.
(erc-match-message/pal/all, erc-match-message/fool/all)
(erc-match-message/dangerous-host/all): New tests.
(erc-match-tests--hl-type-nick-or-keyword): New function.
(erc-match-message/current-nick/nick-or-keyword): New test.
(erc-match-tests--hl-type-keyword): New function.
(erc-match-message/keyword/keyword): New test.
(erc-match-tests--log-matches): New function.
(erc-log-matches): New test.
* test/lisp/erc/resources/erc-tests-common.el: Require `erc-d-i'.
(erc-tests-common-add-cmem, erc-tests-common-parse-line)
(erc-tests-common-simulate-line)
(erc-tests-common-simulate-privmsg): New functions.

(cherry picked from commit 9bddb264ba851f39068773b9538de4170928e159)