Parse provider IDs from season and episode folder/file names

Season and episode directories/files can now include provider ID
attributes in their names (e.g. "Season 01 [tvdbid=22222]" or
"Show S01E01 [tmdbid=99999].mkv"), consistent with the existing
behavior for series folders.

Supported providers: imdbid, tvdbid, tvmazeid, tmdbid.

Adds TmdbSeasonExternalId and TmdbEpisodeExternalId so that
the TMDB season and episode IDs are surfaced in the metadata editor.

Seasons do not have their own IMDb IDs, so we don't support imdbid parsing
in SeasonResolver. Instead, generate IMDb season URLs via
ImdbExternalUrlProvider using the parent series' IMDb ID and the
season number, matching the IMDb URL format:
imdb.com/title/{seriesId}/episodes/?season={N}

Add tests for the ExternalUrlProviders.

MediaBrowser.Providers/Movies/ImdbExternalUrlProvider.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using MediaBrowser.Controller.Entities;
+using MediaBrowser.Controller.Entities.TV;
 using MediaBrowser.Controller.Providers;
 using MediaBrowser.Model.Entities;
 
@@ -17,6 +18,18 @@ public class ImdbExternalUrlProvider : IExternalUrlProvider
     public IEnumerable<string> GetExternalUrls(BaseItem item)
     {
         var baseUrl = "https://www.imdb.com/";
+
+        if (item is Season season)
+        {
+            if (season.Series?.TryGetProviderId(MetadataProvider.Imdb, out var seriesImdbId) == true
+                && season.IndexNumber.HasValue)
+            {
+                yield return baseUrl + $"title/{seriesImdbId}/episodes/?season={season.IndexNumber.Value}";
+            }
+
+            yield break;
+        }
+
         if (item.TryGetProviderId(MetadataProvider.Imdb, out var externalId))
         {
             if (item is Person)

MediaBrowser.Providers/Plugins/Tmdb/TV/TmdbEpisodeExternalId.cs

@@ -0,0 +1,25 @@
+using MediaBrowser.Controller.Entities.TV;
+using MediaBrowser.Controller.Providers;
+using MediaBrowser.Model.Entities;
+using MediaBrowser.Model.Providers;
+
+namespace MediaBrowser.Providers.Plugins.Tmdb.TV
+{
+    /// <summary>
+    /// External id for a TMDb episode.
+    /// </summary>
+    public class TmdbEpisodeExternalId : IExternalId
+    {
+        /// <inheritdoc />
+        public string ProviderName => TmdbUtils.ProviderName;
+
+        /// <inheritdoc />
+        public string Key => MetadataProvider.Tmdb.ToString();
+
+        /// <inheritdoc />
+        public ExternalIdMediaType? Type => ExternalIdMediaType.Episode;
+
+        /// <inheritdoc />
+        public bool Supports(IHasProviderIds item) => item is Episode;
+    }
+}

MediaBrowser.Providers/Plugins/Tmdb/TV/TmdbSeasonExternalId.cs

@@ -0,0 +1,25 @@
+using MediaBrowser.Controller.Entities.TV;
+using MediaBrowser.Controller.Providers;
+using MediaBrowser.Model.Entities;
+using MediaBrowser.Model.Providers;
+
+namespace MediaBrowser.Providers.Plugins.Tmdb.TV
+{
+    /// <summary>
+    /// External id for a TMDb season.
+    /// </summary>
+    public class TmdbSeasonExternalId : IExternalId
+    {
+        /// <inheritdoc />
+        public string ProviderName => TmdbUtils.ProviderName;
+
+        /// <inheritdoc />
+        public string Key => MetadataProvider.Tmdb.ToString();
+
+        /// <inheritdoc />
+        public ExternalIdMediaType? Type => ExternalIdMediaType.Season;
+
+        /// <inheritdoc />
+        public bool Supports(IHasProviderIds item) => item is Season;
+    }
+}

MediaBrowser.Providers/Plugins/Tmdb/TV/TmdbSeriesExternalId.cs

@@ -20,9 +20,6 @@ namespace MediaBrowser.Providers.Plugins.Tmdb.TV
         public ExternalIdMediaType? Type => ExternalIdMediaType.Series;
 
         /// <inheritdoc />
-        public bool Supports(IHasProviderIds item)
-        {
-            return item is Series;
-        }
+        public bool Supports(IHasProviderIds item) => item is Series;
     }
 }