### 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
command_line_strings.push_back("--xr_mode_openxr");
	} else { 
		command_line_strings.push_back("--xr_mode_regular");
	}
	bool immersive = p_preset->get("screen/immersive_mode");
	if (immersive) {
		command_line_strings.push_back("--use_immersive");
	}
	bool debug_opengl = p_preset->get("graphics/opengl_debug");
	if (debug_opengl) {
		command_line_strings.push_back("--debug_opengl");
	}
	if (command_line_strings.size()) {
		r_command_line_flags.resize(4);
		encode_uint32(command_line_strings.size(), &r_command_line_flags.write[0]);
		for (int i = 0; i < command_line_strings.size(); i++) {
			print_line(itos(i) + " param: " + command_line_strings[i]);
			CharString command_line_argument = command_line_strings[i].utf8();
			int base = r_command_line_flags.size();
			int length = command_line_argument.length();
			if (length == 0) {
				continue;
			}
			r_command_line_flags.resize(base + 4 + length);
			encode_uint32(length, &r_command_line_flags.write[base]);
			memcpy(&r_command_line_flags.write[base + 4], command_line_argument.ptr(), length);
		}
	}
}
Error EditorExportPlatformAndroid::sign_apk(const Ref<EditorExportPreset> &p_preset, bool p_debug, const String &export_path, EditorProgress &ep) {