The hash is used to check whether the arginfo file needs to be
regenerated. PHP-Parser will only be downloaded if this is actually
necessary.
This ensures that release artifacts will never try to regenerate
stubs and thus fetch PHP-Parser, as long as you do not modify any
files.
Closes GH-5739.
The `$prefix` parameter of `xmlwriter_write_element_ns()` and
`xmlwriter_start_element_ns()` is nullable, what allows these functions
to be used instead of their non NS variants. Consequently, we make the
`$prefix` parameter of `xmlwriter_write_attribute_ns()` and
`xmlwriter_start_attribute_ns()` nullable as well.
