It is somewhat unintuitive that parse_str() is subject to the
max_input_vars limitation and there are sites that use parse_str() to
parse things that aren't directly coming from user query args.
There arr two ways to solve this. We could add an optional max_vars arg
something along these lines:
The other way to solve this would be to make max_input_vars PHP_INI_ALL
and then just let people ini_set() their way around the limit.
The one drawback with the optional arg approach is that since
parse_str() is a thin layer on top of the query string parser, the error
if you exceed the passed max_vars talks about the ini setting which in
this case wouldn't really be correct and fixing that would be complicated.