flutter: Renamed KDDockWidgets package to KDDockWidgetsBindings

The former is needed for the KDDW flutter frontend, which will use
the latter to access the C++ API.

Using two packages instead of one, since one is generated by
dartagnan.

src/flutter/generated/KDDockWidgetsBindings/dart/lib/Bindings.dart

@@ -0,0 +1,57 @@
+/*
+  This file is part of KDDockWidgets.
+
+  SPDX-FileCopyrightText: 2019-2022 Klarälvdalens Datakonsult AB, a KDAB Group company <info@kdab.com>
+  Author: Sérgio Martins <sergio.martins@kdab.com>
+
+  SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only
+
+  Contact KDAB at <info@kdab.com> for commercial licensing options.
+*/
+export 'src/Platform.dart' show Platform;
+export 'src/View.dart' show View;
+export 'src/ViewFactory.dart' show ViewFactory;
+export 'src/QByteArray.dart' show QByteArray;
+export 'src/QList.dart' show QList;
+export 'src/QObject.dart' show QObject;
+export 'src/QPoint.dart' show QPoint;
+export 'src/QRect.dart' show QRect;
+export 'src/QSize.dart' show QSize;
+export 'src/QString.dart' show QString;
+import 'dart:ffi' as ffi;
+import 'dart:io' show Platform;
+
+String bindingsLibraryName(String name) {
+  if (Platform.isWindows) return "${name}.dll";
+  if (Platform.isMacOS) return "lib${name}.dylib";
+  return "lib${name}.so";
+}
+
+class Library {
+  var _dylib;
+
+  ffi.DynamicLibrary get dylib {
+    return _dylib;
+  }
+
+  static var _library = null;
+
+  factory Library.instance() {
+    // Singleton impl.
+    if (_library == null) _library = Library._();
+    return _library;
+  }
+
+  Library._() {
+    // DYLD_LIBRARY_PATH doesn't work by default on newer macOS. Instead
+    // introduce our own env variable for the same use case
+    var bindingsPath = Platform.environment["DARTAGNAN_BINDINGSLIB_PATH"] ?? "";
+
+    var libraryPath = bindingsLibraryName("kddockwidgets");
+    if (!bindingsPath.isEmpty) {
+      libraryPath = bindingsPath + "/" + libraryPath;
+    }
+
+    _dylib = ffi.DynamicLibrary.open(libraryPath);
+  }
+}