### 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
Vector<PluginConfigAndroid> plugins;
	String last_plugin_names;
	uint64_t last_custom_build_time = 0;
	SafeFlag plugins_changed;
	Mutex plugins_lock;
	Vector<Device> devices;
	SafeFlag devices_changed;
	Mutex device_lock;
#ifndef ANDROID_ENABLED
	Thread check_for_changes_thread;
	SafeFlag quit_request;
	static void _check_for_changes_poll_thread(void *ud);
#endif
	String get_project_name(const String &p_name) const;
	String get_package_name(const String &p_package) const;
	String get_assets_directory(const Ref<EditorExportPreset> &p_preset, int p_export_format) const;
	bool is_package_name_valid(const String &p_package, String *r_error = nullptr) const;
	static bool _should_compress_asset(const String &p_path, const Vector<uint8_t> &p_data);
	static zip_fileinfo get_zip_fileinfo();
	struct ABI {
		String abi;
		String arch;
		bool operator==(const ABI &p_a) const {
			return p_a.abi == abi;
		}
		ABI(const String &p_abi, const String &p_arch) {
			abi = p_abi;
			arch = p_arch;
		}
		ABI() {}