[Core + Framework] Performance improvements for re-drawing the grid (#141)

This proposes a *new method* on IObservatoryCore:  `SetGridItems(worker, items)` which does 2 things:
* Clears the grid
* Adds the given items.

Effectively replaces the entire content of the grid -- which is something a handful of plugins now do.

Why add this when you could just call Core's Clear + AddGridItems methods?? So it can all be done within the same rendering suppression "scope" to reduce flickering and increase rendering speed.  Speaking of rendering suppression, I have implemented such rendering suppression "scope" which uses Listview's built-in Begin/EndUpdate() in combination with temporary removal of the sort comparer (as is done for read-alls).  This was also applied to the existing AddGridItems(worker, items) method as well, addressing a TODO.

ObservatoryCore/PluginManagement/PluginCore.cs

@@ -2,6 +2,7 @@
 using Observatory.Framework.Files;
 using Observatory.Framework.Interfaces;
 using Observatory.NativeNotification;
+using Observatory.UI;
 using Observatory.Utils;
 using System;
 using System.Collections.ObjectModel;
@@ -114,11 +115,27 @@ namespace Observatory.PluginManagement
 
         public void AddGridItems(IObservatoryWorker worker, IEnumerable<object> items)
         {
-            //TODO: Use better bulk handling here.
+            BeginBulkUpdate(worker);
+
             foreach (var item in items)
             {
                 worker.PluginUI.DataGrid.Add(item);
             }
+
+            EndBulkUpdate(worker);
+        }
+
+        public void SetGridItems(IObservatoryWorker worker, IEnumerable<object> items)
+        {
+            BeginBulkUpdate(worker);
+
+            worker.PluginUI.DataGrid.Clear();
+            foreach (var item in items)
+            {
+                worker.PluginUI.DataGrid.Add(item);
+            }
+
+            EndBulkUpdate(worker);
         }
 
         public void ClearGrid(IObservatoryWorker worker, object templateItem)
@@ -186,5 +203,40 @@ namespace Observatory.PluginManagement
         {
             NativePopup.CloseAll();
         }
+
+        private void BeginBulkUpdate(IObservatoryWorker worker)
+        {
+            PluginListView? listView = FindPluginListView(worker);
+            if (listView == null) return;
+
+            ExecuteOnUIThread(() => { listView.SuspendDrawing(); });
+        }
+
+        private void EndBulkUpdate(IObservatoryWorker worker)
+        {
+            PluginListView? listView = FindPluginListView(worker);
+            if (listView == null) return;
+
+            ExecuteOnUIThread(() => { listView.ResumeDrawing(); });
+        }
+
+        private PluginListView? FindPluginListView(IObservatoryWorker worker)
+        {
+            if (worker.PluginUI.PluginUIType != PluginUI.UIType.Basic
+                || !(worker.PluginUI.UI is Panel)) return null;
+
+            PluginListView? listView = null;
+            Panel panel = worker.PluginUI.UI as Panel;
+
+            foreach (var control in panel.Controls)
+            {
+                if (control?.GetType() == typeof(PluginListView))
+                {
+                    listView = (PluginListView)control;
+                    return listView;
+                }
+            }
+            return null;
+        }
     }
 }

ObservatoryCore/UI/PluginHelper.cs

@@ -61,6 +61,7 @@ namespace Observatory.UI
             {
                 Anchor = AnchorStyles.Left | AnchorStyles.Right | AnchorStyles.Bottom | AnchorStyles.Top
             };
+            plugin.PluginUI.UI = panel;
 
             IObservatoryComparer columnSorter;
             if (plugin.ColumnSorter != null)

ObservatoryCore/UI/PluginListView.cs

@@ -1,20 +1,17 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.InteropServices;
 using System.Security.Permissions;
 using System.Text;
 using System.Threading.Tasks;
+using System.Windows.Forms;
 
 namespace Observatory.UI
 {
     internal class PluginListView : ListView
     {
-        [DllImport("user32.dll")]
-        private static extern int SendMessage(IntPtr hWnd, int wMsg, bool wParam, int lParam);
-        
-        private const int WM_SETREDRAW = 11;
-
         public PluginListView()
         {
             OwnerDraw = true;
@@ -28,6 +25,25 @@ namespace Observatory.UI
             base.GridLines = false;//We should prevent the default drawing of gridlines.
         }
 
+        // Stash for performance when doing large UI updates.
+        private IComparer? comparer = null;
+
+        public void SuspendDrawing()
+        {
+            BeginUpdate();
+            comparer = ListViewItemSorter;
+        }
+
+        public void ResumeDrawing()
+        {
+            if (comparer != null)
+            {
+                ListViewItemSorter = comparer;
+                comparer = null;
+            }
+            EndUpdate();
+        }
+
         private static void DrawBorder(Graphics graphics, Pen pen, Rectangle bounds, bool header = false)
         {