vk_command_pool: Move definition of Pool into the cpp file

Allows the implementation details to be changed without recompiling any
files that include this header.

src/video_core/renderer_vulkan/vk_command_pool.cpp

@@ -12,6 +12,11 @@ namespace Vulkan {
 
 constexpr size_t COMMAND_BUFFER_POOL_SIZE = 0x1000;
 
+struct CommandPool::Pool {
+    vk::CommandPool handle;
+    vk::CommandBuffers cmdbufs;
+};
+
 CommandPool::CommandPool(MasterSemaphore& master_semaphore, const VKDevice& device)
     : ResourcePool(master_semaphore, COMMAND_BUFFER_POOL_SIZE), device{device} {}
 

src/video_core/renderer_vulkan/vk_command_pool.h

@@ -25,10 +25,7 @@ public:
     VkCommandBuffer Commit();
 
 private:
-    struct Pool {
-        vk::CommandPool handle;
-        vk::CommandBuffers cmdbufs;
-    };
+    struct Pool;
 
     const VKDevice& device;
     std::vector<Pool> pools;