[mlir][vector][nvgpu] Move MMA contraction preparation to VectorUtils
This pattern is not specific to nvgpu; I intend to use in SPIR-V codegen. `VectorTransforms` seems like a more generally useful place.
In addition:
- Fix a bug in the second condition (the dimensions were swapped for RHS).
- Add tests.
- Add support for externally provided filter functions, similar to other vector transforms.
- Prefer to transpose before zero/sign-extending inputs.
Reviewed By: ThomasRaoux
Differential Revision: https://reviews.llvm.org/D145638