[FancyZones] Rework grid editor (#10116)

* Started rewriting

* Making progress

* Fix resizers not moving around

* Implemented splitting, fixed some bugs

* Removed more code, renamed methods

* Merging zones works

* Fix Shift key behavior

* Added spacing (has bugs)

* Implement minimum size restriction

* Match preview and editor visuals

* Snapping works

* Show when splitting is not possible

* Fix spell checker complaining

* Tweak FZ Lib function computing grid zones

* Fix potential crash when loading old zone layouts

* Fix dead objects talking

* Fix splitters being shown when they shouldn't be

* Fix index numbering

* Fix small glitch with the shift key

* Do not snap to borders outside the zone

src/modules/fancyzones/editor/FancyZonesEditor/MagneticSnap.cs

@@ -0,0 +1,79 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace FancyZonesEditor
+{
+    public class MagneticSnap
+    {
+        private List<int> _keyPoints;
+        private double _workAreaSize;
+
+        private const int MagnetZoneMaxSize = GridData.Multiplier / 12;
+
+        public MagneticSnap(List<int> keyPoints, double workAreaSize)
+        {
+            _keyPoints = keyPoints;
+            _workAreaSize = workAreaSize;
+        }
+
+        public int PixelToDataWithSnapping(double pixel, int low, int high)
+        {
+            var keyPoints = _keyPoints.Where(x => low < x && x < high).ToList();
+            var magnetZoneSizes = new List<int>();
+
+            for (int i = 0; i < keyPoints.Count; i++)
+            {
+                int previous = i == 0 ? low : keyPoints[i - 1];
+                int next = i == keyPoints.Count - 1 ? high : keyPoints[i + 1];
+                magnetZoneSizes.Add(Math.Min(keyPoints[i] - previous, Math.Min(next - keyPoints[i], MagnetZoneMaxSize)) / 2);
+            }
+
+            int data = Convert.ToInt32(pixel / _workAreaSize * GridData.Multiplier);
+            data = Math.Clamp(data, low, high);
+            int result;
+            int snapId = -1;
+
+            for (int i = 0; i < keyPoints.Count; ++i)
+            {
+                if (Math.Abs(data - keyPoints[i]) <= magnetZoneSizes[i])
+                {
+                    snapId = i;
+                    break;
+                }
+            }
+
+            if (snapId == -1)
+            {
+                result = data;
+            }
+            else
+            {
+                int deadZoneWidth = (magnetZoneSizes[snapId] + 1) / 2;
+                if (Math.Abs(data - keyPoints[snapId]) <= deadZoneWidth)
+                {
+                    result = keyPoints[snapId];
+                }
+                else if (data < keyPoints[snapId])
+                {
+                    result = data + (data - (keyPoints[snapId] - magnetZoneSizes[snapId]));
+                }
+                else
+                {
+                    result = data - ((keyPoints[snapId] + magnetZoneSizes[snapId]) - data);
+                }
+            }
+
+            return Math.Clamp(result, low, high);
+        }
+
+        public double DataToPixelWithoutSnapping(int data)
+        {
+            return _workAreaSize * data / GridData.Multiplier;
+        }
+    }
+}