[C++][GPU] Writing sliced GPU record batches to IPC

### Describe the enhancement requested

Currently, it isn't possible to write GPU-memory backed record batches to IPC if they are sliced. When Arrays are sliced, the null-count is set to a sentinel to indicate "UNKNOWN" rather than recompute it immediately. We need to add some interfaces to the GPU / MemoryManager / Device libraries to perform the bit counting and copying of bitmaps to handle sliced arrays properly and write them to IPC when they are using device memory.

### Component(s)

C++, GPU