Rewrite host GPU abstraction

- Don't have to repeat the same thing for 4 renderers.
 - Add native Metal renderer.

src/util/vulkan_entry_points.h

@@ -0,0 +1,20 @@
+// SPDX-FileCopyrightText: 2019-2023 Connor McLaughlin <stenzek@gmail.com>
+// SPDX-License-Identifier: (GPL-3.0 OR CC-BY-NC-ND-4.0)
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define VULKAN_MODULE_ENTRY_POINT(name, required) extern PFN_##name name;
+#define VULKAN_INSTANCE_ENTRY_POINT(name, required) extern PFN_##name name;
+#define VULKAN_DEVICE_ENTRY_POINT(name, required) extern PFN_##name name;
+#include "vulkan_entry_points.inl"
+#undef VULKAN_DEVICE_ENTRY_POINT
+#undef VULKAN_INSTANCE_ENTRY_POINT
+#undef VULKAN_MODULE_ENTRY_POINT
+
+#ifdef __cplusplus
+}
+#endif