code: Use std::span where appropriate (#6658)

* code: Use std::span when possible

* code: Prefix memcpy and memcmp with std::

src/video_core/renderer_vulkan/vk_instance.h

@@ -181,7 +181,7 @@ public:
     }
 
     /// Returns the list of available extensions.
-    const std::vector<std::string>& GetAvailableExtensions() const {
+    std::span<const std::string> GetAvailableExtensions() const {
         return available_extensions;
     }