feat: expose state in ImagePicker previewBuilder

Enables custom previewBuilder implementations to access validation state
and error messages. This makes it possible to display validation errors
with custom preview layouts, which wasn't previously possible.

Signed-off-by: Ricardo <[email protected]>

Author: ricpar11

lib/src/form_builder_image_picker.dart

@@ -42,6 +42,7 @@ class FormBuilderImagePicker extends FormBuilderFieldDecoration<List<dynamic>> {
     BuildContext,
     List<Widget> children,
     Widget? addButton,
+    FormBuilderImagePickerState state,
   )? previewBuilder;
 
   /// placeholder image displayed when picking a new image
@@ -332,6 +333,7 @@ class FormBuilderImagePicker extends FormBuilderFieldDecoration<List<dynamic>> {
                   context,
                   widgets,
                   canUpload ? addButtonBuilder(context) : null,
+                  state,
                 );
               });
             }