[mlir][nfc] Update vectorize-tensor-extract.mlir (2/N)

Tests in "vectorize-tensor-extract.mlir" are inconsistent and would
benefit from refactoring to:

* Clearly categorize tests into "contiguous load," "gather load," and
  "scalar load + broadcast" cases, reflecting the structure of
  tensor.extract vectorization.
* Unify variable naming (both MLIR and FileCheck).
* Ensure all tests exercise unmasked vectorization (masked vectorization
  is covered in "vectorize-tensor-extract-masked.mlir").
* Improve and standardize formatting.

These changes will make it easier to identify the test cases being
exercised and simplify future maintenance or refactoring.

This is patch 2/N in the series. Below is a summary of the changes in
this patch.

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Summary of patch 2/N
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Makes all tests re-use the same TD sequence. This TD sequence has been
extracted to a dedicted file:
  * "td/vectorize-with-patterns.mlir".

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**DEPENDS ON**
* llvm#118977
* llvm#119079

Please only review the top commit

Author: banach-space

mlir/test/Dialect/Linalg/td/vectorize-with-patterns.mlir

@@ -0,0 +1,10 @@
+module @transforms attributes { transform.with_named_sequence } {
+  transform.named_sequence @vectorize_with_patterns(%module: !transform.any_op {transform.readonly}) {
+
+    %0 = transform.structured.match ops{["linalg.generic"]} in %module : (!transform.any_op) -> !transform.any_op
+    %1 = transform.get_parent_op %0 {isolated_from_above} : (!transform.any_op) -> !transform.any_op
+    %2 = transform.structured.vectorize_children_and_apply_patterns %1 { vectorize_nd_extract } : (!transform.any_op) -> !transform.any_op
+
+    transform.yield
+   }
+}