[DEPRECATION] ManagedStruct automatic resize on shape change

[plobsing]

Changing the shape of a struct can occur for reasons other than the desire to reallocate, for example, when trying to view contents as different datatypes (emulating perl's pack/unpack).

Also reshapes can take several steps. Reallocating each step is suboptimal. In stead, an allocate/reallocate method should be called after the reshaping is complete to reallocate to the new desired shape.