Add CHM viewer plugin (WebView2-based)

This commit does not implement the file link

QuickLook.Plugin/QuickLook.Plugin.ChmViewer/Helper.cs

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+// Copyright © 2017-2026 QL-Win Contributors
+//
+// This file is part of QuickLook program.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+using System;
+using System.IO;
+using System.Text;
+
+namespace QuickLook.Plugin.ChmViewer;
+
+internal static class Helper
+{
+    public static Uri FilePathToFileUrl(string filePath)
+    {
+        var uri = new StringBuilder();
+        foreach (var v in filePath)
+            if (v >= 'a' && v <= 'z' || v >= 'A' && v <= 'Z' || v >= '0' && v <= '9' ||
+                v == '+' || v == '/' || v == ':' || v == '.' || v == '-' || v == '_' || v == '~' ||
+                v > '\x80')
+                uri.Append(v);
+            else if (v == Path.DirectorySeparatorChar || v == Path.AltDirectorySeparatorChar)
+                uri.Append('/');
+            else
+                uri.Append($"%{(int)v:X2}");
+        if (uri.Length >= 2 && uri[0] == '/' && uri[1] == '/') // UNC path - Universal Naming Convention
+            uri.Insert(0, "file:");
+        else
+            uri.Insert(0, "file:///");
+
+        try
+        {
+            return new Uri(uri.ToString());
+        }
+        catch
+        {
+            return null;
+        }
+    }
+}