Centralizing QArrayData memory management decisions in one place will
allow us to be smarter in how we allocate header and data.
At the moment, these are allocated as a single block. In the future we
may decide to allocate them separately for "large" data or specific
alignment requirements.
For users of QArrayData this remains transparent and not part of the
ABI. The offset field in QArrayDataHeader enables this.
This also hard-wires allocation of empty arrays to return shared_empty.
Allocating detached headers (e.g., to support fromRawData) will thus
require explicit support.
Change-Id: Icac5a1f51ee7e468c76b4493d29debc18780e5dc
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>