Provide func ptrs for debug marker cmds in capture

Some VR applications use debug markers to identify frame boundaries but
not all VR devices provide support for VK_EXT_debug_marker. With this
change GFXR provides function pointers for the extension's functions
in order to capture the debug marker calls and track VR frames.

Author: davidd-lunarg

framework/decode/vulkan_feature_util.cpp

@@ -43,6 +43,7 @@ GFXRECON_BEGIN_NAMESPACE(feature_util)
 // no longer there)
 std::set<std::string> kIgnorableExtensions = {
     VK_EXT_TOOLING_INFO_EXTENSION_NAME,
+    VK_EXT_DEBUG_MARKER_EXTENSION_NAME,
 };
 
 VkResult GetInstanceLayers(PFN_vkEnumerateInstanceLayerProperties instance_layer_proc,