Bind current erc-response around all handlers

Bind current erc-response around all handlers

* lisp/erc/erc-backend.el (erc--parsed-response): New variable to be
the internal version of the ancient `erc-message-parsed', which is
only available during `erc-display-message', and therefore of somewhat
limited utility.
(erc-call-hooks): Bind `erc--parsed-response' to the parsed
`erc-response' object for the duration of its handling.  Bind
`erc--msg-prop-overrides' around all hooks to allow response handlers
to influence inserted msg props for any `erc-display-message' calls.
(Bug#72736)

(cherry picked from commit 15545e15a343cc45561a3ff6b8ea930835b7ff08)