Optimize Vulkan backend for better CPU performance and less GPU synchronization overhead. (#8943)

* Optimize Vulkan backend for better CPU performance and less GPU synchronization overhead.

- Allocation overhead for the temporary std::vectors was easily detectable with a sampling profiler and simple to remove.
- ggml_vk_sync_buffer introduce a full pipeline sync which has a significant cost on the GPU side, sometimes larger than the actual kernel execution. Adding only barriers for shader read/writes and transfers seems to be sufficient looking at the code which either launches compute kernels or copies tensors.

* Fix small typo

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Co-authored-by: 0cc4m <picard12@live.de>