If the port terminates before Port ! close is issued,
there will be no 'closed' reply, so the old code would
hang. As it turns out there is no way to figure out
if a closed reply is supposed to come as that reply
is sent after all links and monitors are triggered.
So we have to use the synchronous port_close to close
the port.

Store messages for 'rex' and 'error_logger' off heap

OTP-14192

file: match enoent and enotdir in path_open

OTP-14191

Performance for processes that receive huge amounts of
messages can be increased by storing the incoming messages
outside the heap (that avoids copying the message in a
garbage collection).

Two OTP processes that are known to receive many messages
are 'rex' (used by 'rpc') and 'error_logger'.

* legoscia/remove-watchdog-vestiges/PR-1255/OTP-14112:
  Remove vestiges of watchdog support in heart

Hardware watchdog support was removed from heart in R13A, but there were
still some vestiges in the code and the documentation.

- Remove mentions of the HW_WD_DISABLE variable, as it's no longer used.
- Remove the HEART_BEAT_BOOT_DELAY variable, as it was only used for the
  hardware watchdog.