Tether query rolls to channel membership in ERC

Tether query rolls to channel membership in ERC

* lisp/erc/erc-backend.el (erc-server-JOIN): Update query membership
via `erc--ensure-query-member' when someone else joins a channel.
(erc-server-NICK): Update query membership via
`erc--ensure-query-member' after someone else changes their nick.
(erc-server-PRIVMSG): After printing a query message from some other
person, remove their nick's data from the query buffer's user table if
they're "untracked," i.e., not a member of a channel.
(erc-server-263, erc-server-263-functions): New function and variable,
a default response handler and hook for "RPL_TRYAGAIN", which servers
send for things like rejecting "WHO" and "WHOX" responses due to rate
limiting.
(erc-server-311): Fix call to `erc-update-user-nick' so the userhost
login component is no longer supplied as the `info' parameter but
rather, correctly, as the `login'.
(erc--extract-352-full-name): Factor out trailing hop-count and GECOS
parsing for use by overriding handlers or those for adjacent numerics.
(erc-server-352): Refactor to handle asterisk as `channel' parameter,
which indicates a nick rather than a channel target.
(erc-server-366): Update membership in all query buffers via
`erc--ensure-query-members' after all names have been received.
(erc-server-401): Forget a known user completely when the server
reports them as nonexistent.
* lisp/erc/erc-common.el (erc--get-server-user): New function, a thin
wrapper around `erc-get-server-user' for cases were inlining would
require declaring symbols not defined in erc-common.
* lisp/erc/erc.el (erc-channel-members): Mention that instances are
used for query-participant tables as well.
(erc--decouple-query-and-channel-membership-p): New variable, a
compatibility flag to access pre-5.6 query bookkeeping behavior.
(erc--ensure-query-member, erc--ensure-query-members): New functions.
(erc-cmd-QUERY): Ensure parties are present in the query buffer's
membership table if they're known to be on the server by simple virtue
of being present in some joined channel.
(erc-message-english-s352-you): New variable.
* test/lisp/erc/erc-scenarios-base-query-participants.el
(erc-scenarios-base-query-participants)
(erc-scenarios-base-query-participants/legacy): Rename former to
latter.  Enable compat flag to activate legacy query behavior in which
channel membership does not impact query membership.
(erc-scenarios-base-query-participants/coupled): New test asserting
new behavior in which channel membership dictates query
membership.  (Bug#70928)

(cherry picked from commit 04477cf97be9eb2bb5ae09eff114252864461f05)