This allows lowering vector types like: vector<3x[4]> or vector<3x2x[4]> to LLVM IR, i.e. vectors where the trailing dim is scalable. This is contingent on: https://discourse.llvm.org/t/rfc-enable-arrays-of-scalable-vector-types/72935 More tests will be added in later patches, however, some MLIR fixes are needed first. Depends on: D158517 Reviewed By: awarzynski Differential Revision: https://reviews.llvm.org/D158752