location just past the end of the previous field in the aggregate. Updated to be just past the end of this field to be placed, i.e. the future nextoffset
size of field
natural alignment of field
alignment in effect for this field
size of aggregate (updated)
alignment of aggregate (updated)
the aggregate is a union
aligned offset to place field at
Place a field (mem) into an aggregate (agg), which can be a struct, union or class