add plugin support for external preview

Author: jjw24

Flow.Launcher.Core/Plugin/PluginManager.cs

@@ -88,6 +88,38 @@ public static async Task ReloadDataAsync()
             }).ToArray());
         }
 
+        public static async Task OpenExternalPreviewAsync(string path, bool sendFailToast = true)
+        {
+            await Task.WhenAll(AllPlugins.Select(plugin => plugin.Plugin switch
+            {
+                IAsyncExternalPreview p => p.OpenPreviewAsync(path, sendFailToast),
+                _ => Task.CompletedTask,
+            }).ToArray());
+        }
+
+        public static async Task CloseExternalPreviewAsync()
+        {
+            await Task.WhenAll(AllPlugins.Select(plugin => plugin.Plugin switch
+            {
+                IAsyncExternalPreview p => p.ClosePreviewAsync(),
+                _ => Task.CompletedTask,
+            }).ToArray());
+        }
+
+        public static async Task SwitchExternalPreviewAsync(string path, bool sendFailToast = true)
+        {
+            await Task.WhenAll(AllPlugins.Select(plugin => plugin.Plugin switch
+            {
+                IAsyncExternalPreview p => p.SwitchPreviewAsync(path, sendFailToast),
+                _ => Task.CompletedTask,
+            }).ToArray());
+        }
+
+        public static bool UseExternalPreview()
+        {
+            return GetPluginsForInterface<IAsyncExternalPreview>().Any(x => !x.Metadata.Disabled);
+        }
+
         static PluginManager()
         {
             // validate user directory

Flow.Launcher.Plugin/Interfaces/IAsyncExternalPreview.cs

@@ -0,0 +1,15 @@
+using System.Threading.Tasks;
+
+namespace Flow.Launcher.Plugin
+{
+    public interface IAsyncExternalPreview: IFeatures
+    {
+        public Task TogglePreviewAsync(string path);
+
+        public Task OpenPreviewAsync(string path, bool sendFailToast = true);
+
+        public Task ClosePreviewAsync();
+
+        public Task SwitchPreviewAsync(string path, bool sendFailToast = true);
+    }
+}