### 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 ret;
	for (int i = 0; i < p_parts.size(); ++i) {
		if (i > 0) {
			ret += p_separator;
		}
		ret += (p_use_arch) ? p_parts[i].arch : p_parts[i].abi;
	}
	return ret;
}
Error EditorExportPlatformAndroid::export_project(const Ref<EditorExportPreset> &p_preset, bool p_debug, const String &p_path, int p_flags) {
	int export_format = int(p_preset->get("custom_build/export_format"));
	bool should_sign = p_preset->get("package/signed");
	return export_project_helper(p_preset, p_debug, p_path, export_format, should_sign, p_flags);
}
Error EditorExportPlatformAndroid::export_project_helper(const Ref<EditorExportPreset> &p_preset, bool p_debug, const String &p_path, int export_format, bool should_sign, int p_flags) {
	ExportNotifier notifier(*this, p_preset, p_debug, p_path, p_flags);
	String src_apk;
	Error err;
	EditorProgress ep("export", TTR("Exporting for Android"), 105, true);
	bool use_custom_build = bool(p_preset->get("custom_build/use_custom_build"));
	bool p_give_internet = p_flags & (DEBUG_FLAG_DUMB_CLIENT | DEBUG_FLAG_REMOTE_DEBUG);
	bool apk_expansion = p_preset->get("apk_expansion/enable");
	Vector<ABI> enabled_abis = get_enabled_abis(p_preset);
	print_verbose("Exporting for Android...");
	print_verbose("- debug build: " + bool_to_string(p_debug));
	print_verbose("- export path: " + p_path);
	print_verbose("- export format: " + itos(export_format));
	print_verbose("- sign build: " + bool_to_string(should_sign));