Add a feature to allow creating Buffers from Vec with custom allocators (allocator_api)

[jhorstmann]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

in #3920 and #3917 support was added to to create buffers from standard Rust vectors. The currently instable allocator_api feature extends Vec to support custom allocators, using functions such as new_in. In our product we are using such custom allocators to track the memory usage of individual queries. I'd like to add a similarly named feature to arrow-rs which would generalize the Buffer::from_vec and MutableBuffer::from_vec functions.

Describe the solution you'd like

• Add a feature named allocator-api to arrow-buffer
• If that feature is active, a different impl of from_vec would be enabled (via cfg attribute), which has a generic parameter for the allocator
• Deallocation::Standard would additionally store the allocator (note the default Global allocator is zero-sized)
• The feature would require a nightly rust compiler, just as the feature of the standard library

Describe alternatives you've considered

Something similar can be achieved using Buffer::from_custom_allocation but requires unsafe and dealing with pointers.

Additional context

[alamb]

In our product we are using such custom allocators to track the memory usage of individual queries. I'd like to add a similarly named feature to arrow-rs which would generalize the Buffer::from_vec and MutableBuffer::from_vec functions.

As @tustvold , @waynexia and I are discovering on #6336, adding the APIs to Buffer and MutableBuffer is just the start -- to really achieve the usecase I think we would need to preserve the allocation information through all the various kernels / transformations that arrow-rs provides.

Also, @haohuaijin offers another potential usecase for this feature that is "accurately track total memory used by multiple arrow arrays that may share the same underlying Buffers (e.g. that were sliced, etc) in #6439