Update on "[ET-VK] Move files using the Vulkan API to vk_api/"

and move from namespace `api` to `vkapi`. This gave me a major headache in the number of places to update.

This stack orgnaizes ET-VK neatly into three abstraction levels, both by folder and by namespace:
1. `namespace vkcompute` and `graph/`: for operator computation implementation and scheduling.
2. `namespace vkcompute::api` and `graph/api/`: for tensor objects (and other objects wrapping our VulkanBuffer/VulkanImage).
3. `namespace vkcompute::vkapi` and `graph/api/vk_api/`: for direct users of Vulkan API

Additionally, we have
- `namespace vkcompute::utils` and `graph/api/utils/`: for utils used by both namespace `api` and `vkapi`

Differential Revision: [D59281539](https://our.internmc.facebook.com/intern/diff/D59281539/)

[ghstack-poisoned]

Author: Jorge Pineda

backends/vulkan/runtime/api/ParamsBuffer.cpp

@@ -8,7 +8,6 @@
 
 #include <executorch/backends/vulkan/runtime/api/ParamsBuffer.h>
 
-#include <cstdint>
 #include <cstring>
 
 namespace vkcompute {