Support for a4w4 (fp4) in block scale gemm AB quant

[ErwinTerpstra]

Proposed changes

Support for packed 4-bit floating point for both A and B tensors in block scale gemm. Tested with A using 1D block scale and B using 2D block scale. Works for both the "regular" and Preshuffle-B pipelines. Note that the regular pipeline stores data in fp8 in LDS (as this is how int4 was implemented). The WP pipeline stores tensor A in fp4 in LDS and dequants in when loading to registers.

Changes include:

• Add fp4 support to ABQuant example, with/without PreshuffleB
• Tests for fp4 on both A and B tensors (a4w4) for base case, irregular sizes and preshuffle B pipeline.
• Other changes:
  • Add support to InterleavedPKTypeLoader for generic type conversions instead of just int4
  • Add LUT for converting fp4 to fp8. Improves performance of 4K tensor by around 25% on gfx12. Disabled by default using TEST_convert_with_table.
  • Some helper traits to work with packed or mixed precision types. Including a method to determine MFMA type based on input types

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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