ShareLinks plugin: guest share links for Jellyfin

Includes fix for redemption failing with DbUpdateConcurrencyException:
change the guest password before applying the user policy, since
UpdatePolicyAsync bumps the user's EF concurrency token and a stale
instance then breaks ChangePassword.

Jellyfin.Plugin.ShareLinks/PluginServiceRegistrator.cs

@@ -0,0 +1,33 @@
+using Jellyfin.Plugin.ShareLinks.Lifecycle;
+using Jellyfin.Plugin.ShareLinks.Services;
+using Jellyfin.Plugin.ShareLinks.Storage;
+using Jellyfin.Plugin.ShareLinks.Web;
+using MediaBrowser.Controller;
+using MediaBrowser.Controller.Plugins;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Jellyfin.Plugin.ShareLinks;
+
+/// <summary>
+/// Registers the foundational ShareLinks services used by later API and web
+/// workers.
+/// </summary>
+public class PluginServiceRegistrator : IPluginServiceRegistrator
+{
+    /// <inheritdoc />
+    public void RegisterServices(IServiceCollection serviceCollection, IServerApplicationHost applicationHost)
+    {
+        _ = applicationHost;
+
+        serviceCollection.AddHostedService<WebInjectionHostedService>();
+        serviceCollection.AddSingleton<ShareLinkStore>();
+        serviceCollection.AddSingleton<ShareTokenService>();
+        serviceCollection.AddSingleton<ItemTagService>();
+        serviceCollection.AddSingleton<JellyfinGuestUserService>();
+        serviceCollection.AddSingleton<ShareLinkCreationService>();
+        serviceCollection.AddSingleton<ShareLinkRedemptionService>();
+        serviceCollection.AddSingleton<ShareLinkCleanupService>();
+        serviceCollection.AddSingleton<IShareLinkCleanupService>(provider => provider.GetRequiredService<ShareLinkCleanupService>());
+        serviceCollection.AddHostedService<StartupCleanupHostedService>();
+    }
+}