Review usage of string.Substring (part 1)

Reduced allocations by replacing string.Substring with ReadOnlySpan<char>.Slice

Emby.Server.Implementations/Library/LibraryManager.cs

@@ -511,8 +511,8 @@ namespace Emby.Server.Implementations.Library
             {
                 // Try to normalize paths located underneath program-data in an attempt to make them more portable
                 key = key.Substring(_configurationManager.ApplicationPaths.ProgramDataPath.Length)
-                    .TrimStart(new[] { '/', '\\' })
-                    .Replace("/", "\\");
+                    .TrimStart('/', '\\')
+                    .Replace('/', '\\');
             }
 
             if (forceCaseInsensitive || !_configurationManager.Configuration.EnableCaseSensitiveItemIds)