libvulkan: refactor for _FORTIFY_SOURCE=3 support.

You can't use malloc_usable_size() when built with _FORTIFY_SOURCE=3, so pull out the allocator into a file that can be built _FORTIFY_SOURCE=2 while still getting the benefits for the rest of the code.

Bug: http://b/291762537
Change-Id: Ic3a71bd8eadeb2da167edc0ba28becba2f95f82e
diff --git a/vulkan/libvulkan/driver.h b/vulkan/libvulkan/driver.h
index 4b855e5..fa85dd5 100644
--- a/vulkan/libvulkan/driver.h
+++ b/vulkan/libvulkan/driver.h
@@ -27,6 +27,7 @@
 #include <vulkan/vulkan.h>
 #include <hardware/hwvulkan.h>
 
+#include "allocator.h"
 #include "api_gen.h"
 #include "driver_gen.h"
 #include "debug_report.h"
@@ -102,7 +103,6 @@
 };
 
 bool OpenHAL();
-const VkAllocationCallbacks& GetDefaultAllocator();
 
 void QueryPresentationProperties(
     VkPhysicalDevice physicalDevice,