Preallocate without PreallocationTools

[lukem12345]

Currently, we have two memory management options, controlled by the preallocate flag:

1. Preallocate using PreallocationTools
2. No preallocation

However, for compatibility purposes, some packages would prefer to have plain Julia arrays.

So, we should add an option to compile that allows for the old behavior.

[jpfairbanks]

# TODO: Should maybe have default CPU generation be Vector with PreallocTools being opt-in

Add a new backend for CPUPreallocationBackend

[lukem12345]

See in light of issue #333