Support localization for content search (backoffice) (#12618)

* Support localization for content search

* Formatting

Co-authored-by: Nikolaj Geisle <70372949+Zeegaan@users.noreply.github.com>

* Review changes

* Review changes

Co-authored-by: kjac <kjn@impact.dk>
Co-authored-by: Nikolaj Geisle <70372949+Zeegaan@users.noreply.github.com>

src/Umbraco.Core/Trees/ISearchableTreeWithCulture.cs

@@ -0,0 +1,21 @@
+using Umbraco.Cms.Core.Models.ContentEditing;
+
+namespace Umbraco.Cms.Core.Trees
+{
+    [Obsolete("This interface will be merged into ISearchableTree in Umbraco 12")]
+    public interface ISearchableTreeWithCulture : ISearchableTree
+    {
+        /// <summary>
+        /// Searches for results based on the entity type
+        /// </summary>
+        /// <param name="query"></param>
+        /// <param name="pageSize"></param>
+        /// <param name="pageIndex"></param>
+        /// <param name="searchFrom">
+        ///     A starting point for the search, generally a node id, but for members this is a member type alias
+        /// </param>
+        /// <param name="culture"></param>
+        /// <returns></returns>
+        Task<EntitySearchResults> SearchAsync(string query, int pageSize, long pageIndex, string? searchFrom = null, string? culture = null);
+    }
+}