[mlir][vector] Add missing tests for populateVectorInsertExtractStridedSliceDecompositionPatterns

[banach-space]

See:

• [mlir][Vector] Fix scalable InsertSlice/ExtractSlice lowering #124861 - in particular this comment
• TODO here: https://github.com/llvm/llvm-project/blob/main/mlir/lib/Dialect/Vector/Transforms/VectorInsertExtractStridedSliceRewritePatterns.cpp#L321

Leaving this as a note for myself.

CC @dcaballe

[llvmbot]

@llvm/issue-subscribers-mlir

Author: Andrzej Warzyński (banach-space)

See: * https://github.com//pull/124861 - in particular this [comment](https://github.com//pull/124861#issuecomment-2627774559) * TODO here: https://github.com/llvm/llvm-project/blob/main/mlir/lib/Dialect/Vector/Transforms/VectorInsertExtractStridedSliceRewritePatterns.cpp#L321

Leaving this as a note for myself.

CC @dcaballe