Add a function to reset memory blocks without freeing them

* This can be used only when all resources are safely freed, but means the
  memory can be re-used.

renderdoc/driver/vulkan/vk_core.h

@@ -590,6 +590,7 @@ private:
   VkDeviceSize m_MemoryBlockSize[arraydim<MemoryScope>()] = {};
 
   void FreeAllMemory(MemoryScope scope);
+  void ResetMemoryBlocks(MemoryScope scope);
   void FreeMemoryAllocation(MemoryAllocation alloc);
 
   // internal implementation - call one of the functions above

renderdoc/driver/vulkan/vk_memory.cpp

@@ -432,6 +432,17 @@ void WrappedVulkan::FreeAllMemory(MemoryScope scope)
   });
 }
 
+void WrappedVulkan::ResetMemoryBlocks(MemoryScope scope)
+{
+  rdcarray<MemoryAllocation> &allocList = m_MemoryBlocks[(size_t)scope];
+
+  if(allocList.empty())
+    return;
+
+  for(MemoryAllocation &alloc : allocList)
+    alloc.offs = 0;
+}
+
 void WrappedVulkan::FreeMemoryAllocation(MemoryAllocation alloc)
 {
   // don't do anything at the moment, we only support freeing the whole scope at once.