fix(agc): clear a reused pooled buffer's unused tail on macOS

MoltenVK has no robustBufferAccess2, so a robust read past the end of a
pooled buffer is clamped into its slot instead of returning zero. A
100-byte buffer placed in a 256-byte slot then read the bytes an earlier
user left there (0xabababab), and agc_driver_pooled_buffer_range failed.
On macOS, when a host-coherent mapped slot is handed to a new buffer,
the bytes past the requested size are cleared to zero.

Linux and Windows compile the same code as before.

core/libs/prx/libSceAgcDriver/Graphics/src/Resources.cpp

@@ -6,11 +6,22 @@
 #include "prx/libSceAgcDriver/Execution/include/GuestMemory.hpp"
 #include <algorithm>
 #include <exception>
+#ifdef __APPLE__
+#include <cstddef>
+#include <cstring>
+#endif
 
 namespace AgcDriver::Graphics {
 
 namespace {
 
+#ifdef __APPLE__
+void ClearPooledTail(void* mapping, std::size_t size, VkDeviceSize mappedBytes, VkMemoryPropertyFlags properties) {
+    if (mapping == nullptr || (properties & VK_MEMORY_PROPERTY_HOST_COHERENT_BIT) == 0 || mappedBytes <= size) return;
+    std::memset(static_cast<std::byte*>(mapping) + size, 0, static_cast<std::size_t>(mappedBytes - size));
+}
+
+#endif
 VkDeviceSize ClassAllocationBytes(const VkMemoryRequirements& requirements, std::size_t capacity) {
     const auto alignment = std::max<VkDeviceSize>(requirements.alignment, 1);
     return std::max<VkDeviceSize>(requirements.size, (static_cast<VkDeviceSize>(capacity) + alignment - 1) / alignment * alignment);
@@ -52,6 +63,9 @@ Buffer::Buffer(const Context& context, std::size_t size, VkBufferUsageFlags usag
         capacity = allocation->bytes;
         offset = allocation->offset;
         slab = allocation->slab;
+#ifdef __APPLE__
+        ClearPooledTail(mapping, size, std::min<VkDeviceSize>(capacity, allocationBytes), properties);
+#endif
         if (allocation->bufferBytes != size) {
             context.Function<PFN_vkDestroyBuffer>("vkDestroyBuffer")(context.device, buffer, nullptr);
             buffer = VK_NULL_HANDLE;
@@ -93,6 +107,9 @@ Buffer::Buffer(const Context& context, std::size_t size, VkBufferUsageFlags usag
             Check(context.Function<PFN_vkBindBufferMemory>("vkBindBufferMemory")(context.device, buffer, memory, offset), "vkBindBufferMemory slab");
             initializeAddress(usage);
             mapping = slot.mapping;
+#ifdef __APPLE__
+            ClearPooledTail(mapping, size, capacity, properties);
+#endif
             ready = true;
             return;
         }