Autosave cannot be disabled
I think this patch should be added to this PR - it's pretty straightforward and fixes a problem introduced here.
Configured file type is not set to GeanyDocument
Does not affect this PR (it works for untitled documents) and was probably present before - I think you can open it once this PR is merged.
File templates are not supported
Alright, maybe I miss something but I think you can determine a non-file-backed documents just by checking if `doc->real_path` is NULL or not. But if you do, it would be best to "convert" such a document to "persistent" only when it gets modified, otherwise the result may be annoying (e.g., in the LSP plugin I show LSP server initialization handshake result in a new document. Unless modified, such documents can be closed in Geany without any warnings and you don't want to save such temporary documents).
In addition, I don't think you could change the "document-new" signal without affecting existing plugins. Also, plugins would have to be modified to use `document_new_file_with_creation_type()` consistently and it's kind of error-prone.
In any case, it can wait until this PR is merged.