loader: vk{Create|Destroy}Instance can have multiple tmp callbacks

loader: vk{Create|Destroy}Instance can have multiple tmp callbacks

During code review of the Android version of the temporary debug_report
callbacks code, it was decided to allow an array of
VkDebugReportCallbackCreateInfoEXT structs to be passed to vkCreateInstance().
This code implements that, using some new utility functions in order to help
keep the code clean.