Optimize batch prefill kernel performance for VECTORIZED_LAYOUT KV cache

[Jeff-Huang]

• Add multi-dimensional page index support (YsGatherDims) in tile_scatter_gather
• Add is_gather_dim() and get_gather_index() for multi-dim page lookup
• Override MakeVDramTileDistribution() for VECTORIZED_LAYOUT to match GEMM's BWarpDstrEncoding (K decomposition: {K2, K0, K1})
• Add GetGemmKDecomposition() to retrieve kABKLane and kKPerThread
• Add static_assert for RowMajor VLayout requirement in batch prefill

Proposed changes

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Checklist

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• I have added tests relevant to the introduced functionality, and the unit tests are passing locally
• I have added the test to REGRESSION_TESTS list defined at the top of CMakeLists.txt in tests/CMakeLists.txt, IF the test takes more than 30 seconds to run.
• I have added inline documentation which enables the maintainers with understanding the motivation
• I have removed the stale documentation which is no longer relevant after this pull request
• (If this change is user-facing) I have added release notes which provide the end users with a brief summary of the improvement from this pull request
• I have run clang-format on all changed files
• Any dependent changes have been merged

Discussion

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[poyenc]

LGTM