[macOS] Mark move-only classes as such

Applies the FML_DISALLOW_COPY_AND_ASSIGN to non-POD types in the macOS
embedder. Specifically the following three accessibility-related
classes:
* FlutterPlatformNodeDelegateMac
* FlutterTextPlatformNode
* AccessibilityBridgeMac

No new tests since no semantic change. Only has the compile-time effect
of preventing copying of classes intended to be move-only.

Author: cbracken

shell/platform/darwin/macos/framework/Source/AccessibilityBridgeMac.h

@@ -94,6 +94,8 @@ class AccessibilityBridgeMac : public AccessibilityBridge {
 
   __weak FlutterEngine* flutter_engine_;
   __weak FlutterViewController* view_controller_;
+
+  FML_DISALLOW_COPY_AND_ASSIGN(AccessibilityBridgeMac);
 };
 
 }  // namespace flutter

shell/platform/darwin/macos/framework/Source/FlutterPlatformNodeDelegateMac.h

@@ -56,6 +56,8 @@ class FlutterPlatformNodeDelegateMac : public FlutterPlatformNodeDelegate {
       const gfx::RectF& local_bounds) const;
   gfx::RectF ConvertBoundsFromScreenToGlobal(
       const gfx::RectF& window_bounds) const;
+
+  FML_DISALLOW_COPY_AND_ASSIGN(FlutterPlatformNodeDelegateMac);
 };
 
 }  // namespace flutter

shell/platform/darwin/macos/framework/Source/FlutterTextInputSemanticsObject.h

@@ -56,6 +56,8 @@ class FlutterTextPlatformNode : public ui::AXPlatformNodeBase {
   /// @brief Detaches the FlutterTextField from the FlutterView if it is not
   ///        already detached.
   void EnsureDetachedFromView();
+
+  FML_DISALLOW_COPY_AND_ASSIGN(FlutterTextPlatformNode);
 };
 
 }  // namespace flutter