enable setting output directory for recording

lib/filament_controller.dart

@@ -498,4 +498,9 @@ abstract class FilamentController {
   /// This will impact performance; handle with care.
   ///
   Future setRecording(bool recording);
+
+  ///
+  /// Sets the output directory where recorded PNGs will be placed.
+  ///
+  Future setRecordingOutputDirectory(String outputDirectory);
 }

lib/filament_controller_ffi.dart

@@ -1212,4 +1212,11 @@ class FilamentControllerFFI extends FilamentController {
   Future setRecording(bool recording) async {
     set_recording(_viewer!, recording);
   }
+
+  @override
+  Future setRecordingOutputDirectory(String outputDir) async {
+    var pathPtr = outputDir.toNativeUtf8(allocator: calloc);
+    set_recording_output_directory(_viewer!, pathPtr.cast<Char>());
+    calloc.free(pathPtr);
+  }
 }

lib/generated_bindings.dart

@@ -753,6 +753,14 @@ external void set_recording(
   bool recording,
 );
 
+@ffi.Native<ffi.Void Function(ffi.Pointer<ffi.Void>, ffi.Pointer<ffi.Char>)>(
+    symbol: 'set_recording_output_directory',
+    assetId: 'flutter_filament_plugin')
+external void set_recording_output_directory(
+  ffi.Pointer<ffi.Void> viewer,
+  ffi.Pointer<ffi.Char> outputDirectory,
+);
+
 @ffi.Native<ffi.Void Function()>(
     symbol: 'ios_dummy', assetId: 'flutter_filament_plugin')
 external void ios_dummy();