Update on "[ET-VK] Introduce Vulkan partitioner"

## Context

Introduce `VulkanPartitioner`. I based the implementation of `VulkanPartitioner` on `ArmPartitioner`.

Differential Revision: [D54128090](https://our.internmc.facebook.com/intern/diff/D54128090/)

[ghstack-poisoned]

Author: SS-JIA

backends/vulkan/test/TARGETS

@@ -17,7 +17,6 @@ python_unittest(
         "//executorch/backends/vulkan:vulkan_preprocess",
         "//executorch/backends/vulkan/partitioner:vulkan_partitioner",
         "//executorch/exir:lib",
-        "//executorch/exir/backend:backend_api",
         "//executorch/extension/pybindings:portable_lib",  # @manual
         "//executorch/extension/pytree:pylib",
         "//executorch/kernels/portable:custom_ops_generated_lib",

backends/vulkan/vulkan_preprocess.py

@@ -4,11 +4,10 @@
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
 
-from typing import final, List, Optional
+from typing import final, List
 
 import executorch.backends.vulkan.serialization.vulkan_graph_schema as vk_graph_schema
 
-import torch
 from executorch.backends.vulkan.serialization.vulkan_graph_builder import VkGraphBuilder
 from executorch.backends.vulkan.serialization.vulkan_graph_serialize import (
     serialize_vulkan_graph,
@@ -24,10 +23,7 @@
 from executorch.exir.passes import MemoryPlanningPass, SpecPropPass
 
 from executorch.exir.program._program import _copy_module
-from executorch.exir.tensor import TensorSpec
 from torch import dtype, float32
-from torch._export.utils import get_buffer, get_param, is_buffer, is_param
-from torch.fx import Node
 
 DEFAULT_DEBUG_HANDLE = 65535