[mlir][vector] Merge accumulator/result transpose into contract

This commit adds a pattern to merge accumulator and result
`vector.transpose` ops into `vector.contract`. This kind of
pattern can be generated for NCHW convolution vectorization,
where we use transposes to convert the 1-D NCW convolution
into NWC during vectorization. Merging the transpose would
mean we can avoid materialize vector extract/insert for
transposes and it makes further vector level transformations
easier.

Reviewed By: ThomasRaoux

Differential Revision: https://reviews.llvm.org/D135496