### 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
String fullpath = get_apk_expansion_fullpath(p_preset, p_path);
	Error err = save_pack(p_preset, p_debug, fullpath);
	return err;
}
void EditorExportPlatformAndroid::get_command_line_flags(const Ref<EditorExportPreset> &p_preset, const String &p_path, int p_flags, Vector<uint8_t> &r_command_line_flags) {
	String cmdline = p_preset->get("command_line/extra_args");
	Vector<String> command_line_strings = cmdline.strip_edges().split(" ");
	for (int i = 0; i < command_line_strings.size(); i++) {
		if (command_line_strings[i].strip_edges().length() == 0) {
			command_line_strings.remove_at(i);
			i--;
		}
	}
	gen_export_flags(command_line_strings, p_flags);
	bool apk_expansion = p_preset->get("apk_expansion/enable");
	if (apk_expansion) {
		String fullpath = get_apk_expansion_fullpath(p_preset, p_path);
		String apk_expansion_public_key = p_preset->get("apk_expansion/public_key");
		command_line_strings.push_back("--use_apk_expansion");
		command_line_strings.push_back("--apk_expansion_md5");
		command_line_strings.push_back(FileAccess::get_md5(fullpath));
		command_line_strings.push_back("--apk_expansion_key");
		command_line_strings.push_back(apk_expansion_public_key.strip_edges());
	}
	int xr_mode_index = p_preset->get("xr_features/xr_mode");
	if (xr_mode_index == XR_MODE_OPENXR) {