[mlir][vector] Standardise valueToStore Naming Across Vector Ops (NFC) (#134206)

This change standardises the naming convention for the argument
representing the value to store in various vector operations.
Specifically, it ensures that all vector ops storing a value—whether
into memory, a tensor, or another vector — use `valueToStore` for the
corresponding argument name.

Updated operations:
* `vector.transfer_write`, `vector.insert`, `vector.scalable_insert`,
  `vector.insert_strided_slice`.

For reference, here are operations that currently use `valueToStore`:
* `vector.store` `vector.scatter`, `vector.compressstore`,
  `vector.maskedstore`.

This change is non-functional (NFC) and does not affect the
functionality of these operations.

Implements #131602

mlir/lib/Conversion/VectorToLLVM/ConvertVectorToLLVM.cpp

@@ -1257,7 +1257,7 @@ public:
     // We are going to mutate this 1D vector until it is either the final
     // result (in the non-aggregate case) or the value that needs to be
     // inserted into the aggregate result.
-    Value sourceAggregate = adaptor.getSource();
+    Value sourceAggregate = adaptor.getValueToStore();
     if (insertIntoInnermostDim) {
       // Scalar-into-1D-vector case, so we know we will have to create a
       // InsertElementOp. The question is into what destination.
@@ -1279,7 +1279,8 @@ public:
       }
       // Insert the scalar into the 1D vector.
       sourceAggregate = rewriter.create<LLVM::InsertElementOp>(
-          loc, sourceAggregate.getType(), sourceAggregate, adaptor.getSource(),
+          loc, sourceAggregate.getType(), sourceAggregate,
+          adaptor.getValueToStore(),
           getAsLLVMValue(rewriter, loc, positionOfScalarWithin1DVector));
     }
 
@@ -1305,7 +1306,7 @@ struct VectorScalableInsertOpLowering
   matchAndRewrite(vector::ScalableInsertOp insOp, OpAdaptor adaptor,
                   ConversionPatternRewriter &rewriter) const override {
     rewriter.replaceOpWithNewOp<LLVM::vector_insert>(
-        insOp, adaptor.getDest(), adaptor.getSource(), adaptor.getPos());
+        insOp, adaptor.getDest(), adaptor.getValueToStore(), adaptor.getPos());
     return success();
   }
 };