[mlir][vector] Move splitting transfer ops into a separate entry point

These patterns unrolls transfer read/write ops if the vector consumers/
producers are extract/insert slices op. Transfer ops can map to hardware
load/store functionalities, where the vector size matters for bandwidth
considerations. So these patterns should be collected separately, instead
of being generic canonicalization patterns.

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D96782