### 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
target_sdk_int = target_sdk_str.to_int();
			if (target_sdk_int > DEFAULT_TARGET_SDK_VERSION) {
				
				err += vformat(TTR("\"Target SDK\" %d is higher than the default version %d. This may work, but wasn't tested and may be unstable."), target_sdk_int, DEFAULT_TARGET_SDK_VERSION);
				err += "\n";
			}
		}
	}
	if (target_sdk_int < min_sdk_int) {
		valid = false;
		err += TTR("\"Target SDK\" version must be greater or equal to \"Min SDK\" version.");
		err += "\n";
	}
	r_error = err;
	return valid;
}
List<String> EditorExportPlatformAndroid::get_binary_extensions(const Ref<EditorExportPreset> &p_preset) const {
	List<String> list;
	list.push_back("apk");
	list.push_back("aab");
	return list;
}
String EditorExportPlatformAndroid::get_apk_expansion_fullpath(const Ref<EditorExportPreset> &p_preset, const String &p_path) {
	int version_code = p_preset->get("version/code");
	String package_name = p_preset->get("package/unique_name");
	String apk_file_name = "main." + itos(version_code) + "." + get_package_name(package_name) + ".obb";
	String fullpath = p_path.get_base_dir().path_join(apk_file_name);
	return fullpath;
}
Error EditorExportPlatformAndroid::save_apk_expansion_file(const Ref<EditorExportPreset> &p_preset, bool p_debug, const String &p_path) {