[mlir][Transform] Add support for mapping to GPU warps and to linear ids
This revisions refactors the implementation of mapping to threads to additionally allow warps and linear ids to be specified.
`warp_dims` is currently specified along with `block_dims` as a transform attribute.
Linear ids on th other hand use the flattened block_dims to predicate on the first (linearized) k threads.
An additional GPULinearIdMappingAttr is added to the GPU dialect to allow specifying loops mapped to this new scheme.
Various implementation and transform op semantics cleanups are also applied.
Reviewed By: ThomasRaoux
Differential Revision: https://reviews.llvm.org/D146130