Ignore erc-reconnect-display after a timeout

Ignore erc-reconnect-display after a timeout

* lisp/erc/erc-backend.el (erc--server-reconnect-display-timer): New
variable to store active timer that, upon firing, zeroes out
`erc--server-last-reconnect-count'.
(erc--server-last-reconnect-on-disconnect): New function to run on
`erc-disconnected-hook'.
(erc--server-last-reconnect-display-reset): New function to ensure the
reconnect-display period ends.
* lisp/erc/erc.el (erc-reconnect-display-timeout): New option to
control how long `erc-reconnect-display' affects the displaying of new
buffers following an automatic reconnection.
(erc-process-input-line): Ensure user input marks the end of the
reconnect-display period.
(erc-cmd-JOIN): Don't bother resetting
`erc--server-last-reconnect-count' because it's now handled by its
sometime caller, `erc-process-input-line'.
(erc-connection-established): Schedule timer and register hook to
reset last-reconnect count and terminate the reconnect-display period.
* test/lisp/erc/erc-scenarios-base-buffer-display.el:
(erc-scenarios-base-buffer-display--reconnect-common): Add new args to
test fixture to allow for asserting display properties at various
stages throughout a session.
(erc-scenarios-base-reconnect-options--buffer,
erc-scenarios-base-buffer-display--defwin-recbury-intbuf): Rename
former to latter and rework to better reflect realistic settings
for the relevant display options.
(erc-scenarios-base-reconnect-options--default,
erc-scenarios-base-buffer-display--defwino-recbury-intbuf): Rename
former to latter and rework to be more realistic.
(erc-scenarios-base-buffer-display--count-reset-timeout): New
test for new option `erc-reconnect-display-timeout'.  (Bug#62833)