vulkan: do not distinguish instance or device LayerRef

Merge Get*LayerRef into GetLayerRef and remove LayerRef::is_instance_.
With the removal, LayerRef::SupportsExtension becomes ambiguous.  Replace
it with FindLayer*Extension.  Remove unused LayerRef::GetName and
LayerRef::GetSpecName while at it.

There should be no user-visible change.

Bug: 27911856
Change-Id: I38340654b52338e9ed46d1c4462a6b254b0cab64
diff --git a/vulkan/libvulkan/layers_extensions.h b/vulkan/libvulkan/layers_extensions.h
index 32e1a67..79fe59d 100644
--- a/vulkan/libvulkan/layers_extensions.h
+++ b/vulkan/libvulkan/layers_extensions.h
@@ -26,26 +26,20 @@
 
 class LayerRef {
    public:
-    LayerRef(const Layer* layer, bool is_instance);
+    LayerRef(const Layer* layer);
     LayerRef(LayerRef&& other);
     ~LayerRef();
     LayerRef(const LayerRef&) = delete;
     LayerRef& operator=(const LayerRef&) = delete;
 
-    const char* GetName() const;
-    uint32_t GetSpecVersion() const;
-
     // provides bool-like behavior
     operator const Layer*() const { return layer_; }
 
     PFN_vkGetInstanceProcAddr GetGetInstanceProcAddr() const;
     PFN_vkGetDeviceProcAddr GetGetDeviceProcAddr() const;
 
-    bool SupportsExtension(const char* name) const;
-
    private:
     const Layer* layer_;
-    bool is_instance_;
 };
 
 void DiscoverLayers();
@@ -61,8 +55,12 @@
 const VkExtensionProperties* GetLayerDeviceExtensions(const Layer& layer,
                                                       uint32_t& count);
 
-LayerRef GetInstanceLayerRef(const Layer& layer);
-LayerRef GetDeviceLayerRef(const Layer& layer);
+const VkExtensionProperties* FindLayerInstanceExtension(const Layer& layer,
+                                                        const char* name);
+const VkExtensionProperties* FindLayerDeviceExtension(const Layer& layer,
+                                                      const char* name);
+
+LayerRef GetLayerRef(const Layer& layer);
 
 }  // namespace api
 }  // namespace vulkan