Prep Attribute class for partial update

[Pessimistress]

For #1576

Change List

• Avoid calculating buffer props unless needed
• Only upload changed subarray on attribute update

[Pessimistress]

@ibgreen @tsherif This is the part I'm hoping to get some ideas - in the incremental update use case (e.g. data loaded by chunks), every time we reallocate the buffer, we need to re-upload the entire value array.

[tsherif]

Is it possible to know ahead of time in that incremental case what the total size of the data will be?

[Pessimistress]

Generally, no.

Alternatively, every time overflow happens, we could over-allocate the buffer instead of setting it to the exact new size.

[tsherif]

That makes sense to me. Something like doubling the size of the buffer on each overflow.

[Pessimistress]

How sensitive should we be regarding GPU memory usage?

[tsherif]

It could be a problem on mobile, but I think we have some leeway because we don't use textures much. It would be helpful to profile some typical use cases and see what our current memory usage is like.