Use ArgumentNullException.ThrowIfNull helper method

Did a simple search/replace on the whole repo (except the RSSDP project)
This reduces LOC and should improve performance (methods containing a throw statement don't get inlined)

```
if \((\w+) == null\)
\s+\{
\s+throw new ArgumentNullException\((.*)\);
\s+\}
```

```
ArgumentNullException.ThrowIfNull($1);
```

src/Jellyfin.Extensions/EnumerableExtensions.cs

@@ -18,10 +18,7 @@ namespace Jellyfin.Extensions
         /// <exception cref="ArgumentNullException">The source is null.</exception>
         public static bool Contains(this IEnumerable<string> source, ReadOnlySpan<char> value, StringComparison stringComparison)
         {
-            if (source == null)
-            {
-                throw new ArgumentNullException(nameof(source));
-            }
+            ArgumentNullException.ThrowIfNull(source);
 
             if (source is IList<string> list)
             {