* allow the user to specify a folder where files that can be sent
via LOAD DATA LOCAL can exist
* add mysqli.local_infile_directory for mysqli
(ignored if mysqli.allow_local_infile is enabled)
* add PDO::MYSQL_ATTR_LOCAL_INFILE_DIRECTORY for pdo_mysql
(ignored if PDO::MYSQL_ATTR_LOCAL_INFILE is enabled)
* add related tests
* fixes for building with libmysql 8.x
* small improvement in existing tests
* update php.ini-[development|production] files
Closes GH-6448.
Co-authored-by: Nikita Popov <nikic@php.net>