Make the the data modelling structures model their "real" counterparts
more closely, allowing the user greater control on the produced data.
The changes:
* Add timestamp to atomic_value (which is now a struct, not just an
alias to bytes).
* Add tombstone to collection.
* Add row_tombstone to row.
* Add bound kinds and tombstone to range_tombstone.
Great care was taken to preserve backward compatibility, to avoid
unnecessary changes in existing code.
Both cql3_type and abstract_type are normally used inside
shared_ptr. This creates a problem when an abstract_type needs to refer
to a cql3_type as that creates a cycle.
To avoid warnings from asan, we were using a std::unordered_map to
store one of the edges of the cycle. This avoids the warning, but
wastes even more memory.
Even before this patch cql3_type was a fairly light weight
structure. This patch pushes in that direction and now cql3_type is a
struct with a single member variable, a data_type.
This avoids the reference cycle and is easier to understand IMHO.
Tests: unit (dev)
Signed-off-by: Rafael Ávila de Espíndola <espindola@scylladb.com>
