[mlir][test] Rename Vector integration tests for CPU (nfc) (#93521)

To keep the test filenames consistent, this patch:
  * removes "test-" from  file names (there used to be a mix of
    "test-feature-1.mlir" and "feature-2.mlir"),
  * replaces "_" with "-" (there used to be a mix of "feature-3.mlir"
    and "feature_4.mlir").

Only files under test/Integration/Dialect/Vector/CPU are updated.