[mlir][Linalg] Split vectorization tests

Split Linalg vectorization tests from "vectorization.mlir" across more
specialised test files:
  * vectorize-tensor-extract.mlir - tests for tensor.extract with no
    masking,
  * vectorize-tensor-extract-masked.mlir - tests for tensor.extract with
    masking,
  * vectorization-masked.mlir - all other tests that use masking,
  * vectorisation.mlir - the remaining tests.

Differential Revision: https://reviews.llvm.org/D149843