[mlir][vector] Split populateVectorContractLoweringPatterns

[mlir][vector] Split populateVectorContractLoweringPatterns

It was bundling quite a lot of patterns that convert high-D
vector ops into low-D elementary ops. It might not be good
for all of the patterns to happen for a particular downstream
user. For example, `ShapeCastOpRewritePattern` rewrites
`vector.shape_cast` into data movement extract/insert ops.

Instead, split the entry point into multiple ones so users
can pull in patterns on demand.

Reviewed By: ftynse

Differential Revision: https://reviews.llvm.org/D111225