Otherwise it is hard to uphold the arginfo contract for this
function -- we cannot simply mirror the zpp call, as the class
entry it is based on does not exist.
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.
