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DRW: Batch Cache: Add batch request system

This makes it possible for engines to ask for batches and only fill their
data after all engine populate functions have run.
This means that, when creating the batches data we already know all the
batches that are needed for this redraw and the needed data.

This allows for less redundant data preparation and better attrib masking.
Ideally, we should run all viewports populate function before executing
the batch construction but this is not the scope of this patch.

Conversion from the old request method will be progressive and both can
coexist (see uses of mesh_create_pos_and_nor()).