[mlir][vector] Separate high-D insert/extract strided slice rewrite

Right now `populateVectorInsertExtractStridedSliceTransforms` contains
two categories of patterns, one for decomposing high-D insert/extract
strided slices, the other for lowering them to shuffle ops.
They are at different levels---the former is in the middle, while
the latter is a step of final lowering. Split them to give users
more control of which pattern to pick.

This means break down the previous `VectorExtractStridedSliceOpRewritePattern`,
which is doing two things together.

Also renamed those patterns to be clearer.

Reviewed By: ThomasRaoux

Differential Revision: https://reviews.llvm.org/D123137