Closes GH-6770

When row data split across multiple packets, allocate a temporary
buffer that can be reallocated, and only copy into the row buffer
pool arena once we know the final size. This avoids quadratic
memory usage for very large results.

FilesystemIterator::FOLLOW_SYMLINKS is currently treated as a directory
key mode flag, even though it does not change the way that the key
during iteration is set. To address this, FOLLOW_SYMLINKS has been
converted into an OTHER flag.

Closes GH-6695.

 * 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>

[ci skip]

Signed-off-by: Anatol Belski <ab@php.net>

We should handle the case where the method doesn't exist, and
where it is not visible the same way.

For fake closures, we need to share static variables with the
original function, not work on a separate copy. Calling a function
through Closure::fromCallable() should have the same behavior as
calling it directly.