Merge changes I97efd6c9,I6460f8f0,Ic67e4290,I16214514,Ieaa4e463, ... into nyc-dev
* changes:
vulkan: remove g_device_layers
vulkan: ignore device-only layers
vulkan: ignore layer libraries without instance layers
vulkan: add FindLayer helper
vulkan: constify LayerRef members
vulkan: make g_library_mutex per-LayerLibrary
vulkan: make LayerLibrary a class
vulkan: refactor GetLayerGetProcAddr
vulkan: refactor AddLayerLibrary
vulkan: refactor LayerRef::~LayerRef
vulkan: refactor GetLayerRef
vulkan: add a constructor for LayerLibrary