Improve process doc. with respect to handling of large input (Bug#33191)

* src/process.c (Fprocess_send_region, Fprocess_send_string):
Document that process input longer than the process input
buffer may be split into bunches.  Remove an outdated
reference to a 500 character split boundary.
* doc/lispref/processes.texi (Asynchronous Processes): Remove
mention of "stray character injections" in PTY processes.  See
also the comment about ICANON in src/sysdep.c, function
child_setup_tty.
1 job for emacs-26 in 15 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #359
test

00:00:15

 
Name Stage Failure
failed
test Test There has been a runner system failure, please try again
Running with gitlab-runner 11.4.2 (cf91d5e1)
on gitlab-runner-docker cff9d373
Using Docker executor with image debian:stretch ...
Pulling docker image debian:stretch ...
Using docker image sha256:4879790bd60d439cfe39c063660eef7af525d5f6f1cbb701a14c7cfc11cbfcf7 for debian:stretch ...
ERROR: Job failed (system failure): Error response from daemon: open /var/run/docker/libcontainerd/containerd/8d195b84b28d5b46506bd2396192ce0af96175ed572563534f9f51680eed7f31/init/shim-log.json: no such file or directory (executor_docker.go:1015:3s)