pxweb_data_v2_c: Combine PXWEB API v2 data objects.
Description
Combines a list of pxweb_data_v2 JSON-stat2 data objects returned
from split PXWEB API v2 queries. The combined object keeps the v2 data
shape and rebuilds dimension indexes, labels, sizes, and values so it can be
converted with as.data.frame().