mysqlnd currently sets error_reporting=0 to suppress errors while
writing to streams. Unfortunately these errors are still visible
to userland error handlers, which is a source of confusion.
See for example https://bugs.php.net/bug.php?id=80412.
Instead add a stream flag that suppresses the emission of
read/write errors in the first place, and set it in mysqlnd.
I think it might be useful to have this option for userland as
well in the future, but for now this is just an internal
mechanism.
Closes GH-6458.
24a19cc232