[5.0 -> 1.0] limit the vector size that can be reserved

[greg7mdp]

1.0 merge of AntelopeIO/leap#2405

The deserialization of arrays involves reading a size, and then the array elements which are emplace'd back into a std::vector. For normal vectors, since we know the size in advance, it is beneficial to call std::vector::reserve() to prevent quadratic reallocations of the vector's buffer as the values are read. Still, limit the size that can be reserved to 1024 fc::variant values, or 16KB since sizeof(fc::variant) == 16).

[ericpassmore]

Note:start
group: STABILITY
category: INTERNALS
summary: Limit vector size that can be reserved.
Note:end