[mlir][Linalg] Refactor vectorization of conv1d more aggressively.

This better decouples transfer read/write from vector-only rewrite of conv.
This form is close to ready to plop into a new vector.conv op and the vector.transfer operations to be generalized as part of generic vectorization once the properties ConvolutionOpInterface are inferred from the indexing maps.

This also results in a nice perf boost in the dw == 1 cases.

Differential revision: https://reviews.llvm.org/D112822