add option to record to PNGs (inc background threadpool for encoding)

lib/filament_controller.dart

@@ -492,4 +492,10 @@ abstract class FilamentController {
   ///
   Future<FilamentEntity> getChildEntity(
       FilamentEntity parent, String childName);
+
+  ///
+  /// If [recording] is set to true, each frame the framebuffer/texture will be written to /tmp/output_*.png.
+  /// This will impact performance; handle with care.
+  ///
+  Future setRecording(bool recording);
 }

lib/filament_controller_ffi.dart

@@ -1207,4 +1207,9 @@ class FilamentControllerFFI extends FilamentController {
       calloc.free(childNamePtr);
     }
   }
+
+  @override
+  Future setRecording(bool recording) async {
+    set_recording(_viewer!, recording);
+  }
 }

lib/generated_bindings.dart

@@ -746,6 +746,13 @@ external int find_child_entity_by_name(
   ffi.Pointer<ffi.Char> name,
 );
 
+@ffi.Native<ffi.Void Function(ffi.Pointer<ffi.Void>, ffi.Bool)>(
+    symbol: 'set_recording', assetId: 'flutter_filament_plugin')
+external void set_recording(
+  ffi.Pointer<ffi.Void> viewer,
+  bool recording,
+);
+
 @ffi.Native<ffi.Void Function()>(
     symbol: 'ios_dummy', assetId: 'flutter_filament_plugin')
 external void ios_dummy();