Reuse process in erc-server-delayed-check-reconnect

Reuse process in erc-server-delayed-check-reconnect

* doc/misc/erc.texi (Integrations): Set `erc-server-reconnect-function'
to `erc-server-delayed-check-reconnect' in SOCKS example, and add
definition for `erc-open-socks-tls-stream'.  Mention possible
inaccuracies related to error detection with certain reconnect
strategies.
* lisp/erc/erc-backend.el (erc-server--reconnect-opened): New function.
(erc-server-delayed-check-reconnect): Attempt to reuse process if server
sends a complete PONG, and attempt to accommodate connectors that set
:nowait to nil.
(erc--server-delayed-check-connectors): Remove variable.
(erc-server-prefer-check-reconnect): Inline what was the internal
variable `erc--server-delayed-check-connectors' because it's no longer
used in unit tests.  Add `erc-open-socks-tls-stream' to the set of
connector functions thought to be compatible with the "check" reconnect
strategy.
* test/lisp/erc/erc-scenarios-base-auto-recon.el
(erc-scenarios-base-auto-recon-no-proto): Adapt to expect "reuse" behavior.
* test/lisp/erc/resources/base/reconnect/ping-pong.eld: Delete unused file.
* test/lisp/erc/resources/base/reconnect/unexpected-disconnect.eld:
Capture PING cookie to send back to client.
* test/lisp/erc/resources/erc-d/resources/proxy-solo.eld: Delete unused
file.  (Bug#62044)

(cherry picked from commit f5ebe47ba7723919f09adf8f28d896cfa8757842)