FileManager.createOrUpdateTextFileIfRequired(..) should allow deferred deletes (and use this from AbstractItdMetadataProvider)

Since ROO-1876 it has been possible to defer file updates and creates so that subsequent changes are queued until commit time. Some add-ons (eg addon-tostring) may temporarily not consider they need to produce any members and this leads to a delete operation. The delete isn't a real delete, though, it's simply an interim state until subsequent metadata becomes available and thus an ITD file should be created. It's therefore useful to defer delete operations. This task is to add this capability to FileManager and use it from AbstractItdMetadataProvider.