### Godot version

3.5.1.stable, v4.0.beta.custom_build [0a87ead64]

### System information

Ubuntu 22.04.1

### Issue description

For example, if project has name "300spartans", we can't enter the "org.godotengine.300spartans" to "Unique Name" field. We get the error "Invalid package name: A digit cannot be the first character in a package segment". But , if we enter "org.godotengine.$genname", there will be no error message. When exporting, the name will be set as "org.godotengine.spartans" without "300" in beginning, but user will not be informed about it. I think, it is not very good. It may not be worth making changes to the source code, but mention it in the documentation.

### Steps to reproduce

See issue description.

### Minimal reproduction project

N/A
CLEANUP_AND_RETURN(ERR_SKIP);
	}
	err = OK;
	if (p_flags & DEBUG_FLAG_DUMB_CLIENT) {
		APKExportData ed;
		ed.ep = &ep;
		ed.apk = unaligned_apk;
		err = export_project_files(p_preset, p_debug, ignore_apk_file, &ed, save_apk_so);
	} else {
		if (apk_expansion) {
			err = save_apk_expansion_file(p_preset, p_debug, p_path);
			if (err != OK) {
				add_message(EXPORT_MESSAGE_ERROR, TTR("Export"), TTR("Could not write expansion package file!"));
				return err;
			}
		} else {
			APKExportData ed;
			ed.ep = &ep;
			ed.apk = unaligned_apk;
			err = export_project_files(p_preset, p_debug, save_apk_file, &ed, save_apk_so);
		}
	}
	if (err != OK) {
		unzClose(pkg);
		add_message(EXPORT_MESSAGE_ERROR, TTR("Export"), vformat(TTR("Could not export project files.")));
		CLEANUP_AND_RETURN(ERR_SKIP);
	}
	zip_fileinfo zipfi = get_zip_fileinfo();
	zipOpenNewFileInZip(unaligned_apk,
			"assets/_cl_",