This commit restructures the multidrawable batch set builder for better
performance in various ways:
* The bin traversal is optimized to make the best use of the CPU cache.
* The inner loop that iterates over the bins, which is the hottest part
of `batch_and_prepare_binned_render_phase`, has been shrunk as small as
possible.
* Where possible, multiple elements are added to or reserved from GPU
buffers as a batch instead of one at a time.
* Methods that LLVM wasn't inlining have been marked `#[inline]` where
doing so would unlock optimizations.
This code has also been refactored to avoid duplication between the
logic for indexed and non-indexed meshes via the introduction of a
`MultidrawableBatchSetPreparer` object.
Together, this improved the `batch_and_prepare_binned_render_phase` time
on Caldera by approximately 2×.
Eventually, we should optimize the batchable-but-not-multidrawable and
unbatchable logic as well, but these meshes are much rarer, so in the
interests of keeping this patch relatively small I opted to leave those
to a follow-up.
f15437e4dc