### 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
&zipfi,
			nullptr,
			0,
			nullptr,
			0,
			nullptr,
			0, 
			Z_DEFAULT_COMPRESSION);
	zipWriteInFileInZip(unaligned_apk, command_line_flags.ptr(), command_line_flags.size());
	zipCloseFileInZip(unaligned_apk);
	zipClose(unaligned_apk, nullptr);
	unzClose(pkg);
	if (err != OK) {
		CLEANUP_AND_RETURN(err);
	}
	
	static const int ZIP_ALIGNMENT = 4;
	
	const int next_step = should_sign ? 103 : 105;
	if (ep.step(TTR("Aligning APK..."), next_step)) {
		CLEANUP_AND_RETURN(ERR_SKIP);
	}
	unzFile tmp_unaligned = unzOpen2(tmp_unaligned_path.utf8().get_data(), &io);
	if (!tmp_unaligned) {
		add_message(EXPORT_MESSAGE_ERROR, TTR("Export"), vformat(TTR("Could not unzip temporary unaligned APK.")));
		CLEANUP_AND_RETURN(ERR_FILE_NOT_FOUND);
	}
	ret = unzGoToFirstFile(tmp_unaligned);
	io2 = zipio_create_io(&io2_fa);
	zipFile final_apk = zipOpen2(p_path.utf8().get_data(), APPEND_STATUS_CREATE, nullptr, &io2);