[mlir][vector] Update tests for xfer-permute-lowering (nfc) (#101468)

Updates formatting and variable names in:
  * vector-transfer-permutation-lowering.mlir

This is primarily to improve consistency, both within this particular
test file as well as across tests. In particular, with this PR I'm
adopting similar naming convention to that that's already present in
vector-transfer-flatten.mlir.

Overview of changes:
  * All memref input arguments are re-named as `%mem`.
  * All vector input arguments are re-named as `%vec`.
  * All tensor input arguments are re-named as `%dest`.
  * LIT variables are update to be consistent with input arguments.
  * Renamed all output arguments as `%res`.
  * Updated indentation to be more C-like.

Author: banach-space

mlir/test/Dialect/Vector/vector-transfer-flatten.mlir

@@ -1,6 +1,8 @@
 // RUN: mlir-opt %s -test-vector-transfer-flatten-patterns -split-input-file | FileCheck %s
 // RUN: mlir-opt %s -test-vector-transfer-flatten-patterns=target-vector-bitwidth=128 -split-input-file | FileCheck %s --check-prefix=CHECK-128B
 
+// TODO: Align naming and format with e.g. vector-transfer-permutation-lowering.mlir
+
 ///----------------------------------------------------------------------------------------
 /// vector.transfer_read
 /// [Pattern: FlattenContiguousRowMajorTransferReadPattern]