Deadlock on shutdown with debug callbacks

[etang-cw]

To reproduce:
Run vulkaninfo against MoltenVK

Expected result:
vulkaninfo exits

Actual result:
vulkaninfo doesn't exit
Sampling the process gives this trace (lldb wouldn't attach because annoying macOS restrictions on debugging signed apps):

Seems related to ~MVKInstance logging under _dcbLock

MoltenVK/MoltenVK/MoltenVK/GPUObjects/MVKInstance.mm

Lines 726 to 731 in 568cc3a

	lock_guard<mutex> lock(_dcbLock);
	mvkDestroyContainerContents(_debugReportCallbacks);
	MVKLogInfo("Destroyed VkInstance for Vulkan version %s with %d Vulkan extensions enabled.",
	mvkGetVulkanVersionString(_appInfo.apiVersion).c_str(),
	_enabledExtensions.getEnabledCount());

Not sure whether you meant to log before clearing the debug report callbacks, or to drop the lock before logging, but either of the two should fix it

[billhollings]

PR #2037 fixes this.