This change introduced len/optional attributes for
arrays. Previously, we assumed that these would only
occur on pointers, but now, this information is also
available for arrays.
This adapts the registery and parsing code to also
parse these properly. No modifications are made to the
rendering part as of yet, since these partially filled
arrays cannot be cleanly represented in Zig.
For procedure parameters which are of pointer type: if the associated
`count` parameter is marked `optional` in the XML, this commit makes the
parameter pointer type nullable.
