* vulkan: add hoisting support for row IDs and expert count in shaders
* use hoisted row ids in coopmat2
* vulkan: address review feedback on count_experts
- use vk_op_count_experts_push_constants instead of a raw uint vector
- apply the fastdiv trick to the ne00 div/mod in count_experts
- compute the per-expert offsets with subgroupExclusiveAdd when the
device supports it, keeping the serial path as fallback
- document the data_d layout and the hoisted_row_id_words bound
- drop a leftover debug print in ggml_vk_matmul_id
* vulkan: use init_pushconst_fastdiv for count_experts push constants
* vulkan: refine comments for row ID hoisting and data layout in count_experts shader
* Whitespace
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Co-authored-by: Jeff Bolz <jbolz@nvidia.com>
