### 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
if (abi_index != -1) {
			exported = true;
			String abi = abis[abi_index].abi;
			String dst_path = String("lib").path_join(abi).path_join(p_so.path.get_file());
			Vector<uint8_t> array = FileAccess::get_file_as_bytes(p_so.path);
			Error store_err = store_in_apk(ed, dst_path, array);
			ERR_FAIL_COND_V_MSG(store_err, store_err, "Cannot store in apk file '" + dst_path + "'.");
		}
	}
	if (!exported) {
		ERR_PRINT("Cannot determine architecture for library \"" + p_so.path + "\". One of the supported architectures must be used as a tag: " + join_abis(abis, " ", true));
		return FAILED;
	}
	return OK;
}
Error EditorExportPlatformAndroid::save_apk_file(void *p_userdata, const String &p_path, const Vector<uint8_t> &p_data, int p_file, int p_total, const Vector<String> &p_enc_in_filters, const Vector<String> &p_enc_ex_filters, const Vector<uint8_t> &p_key) {
	APKExportData *ed = static_cast<APKExportData *>(p_userdata);
	String dst_path = p_path.replace_first("res://", "assets/");
	store_in_apk(ed, dst_path, p_data, _should_compress_asset(p_path, p_data) ? Z_DEFLATED : 0);
	return OK;
}
Error EditorExportPlatformAndroid::ignore_apk_file(void *p_userdata, const String &p_path, const Vector<uint8_t> &p_data, int p_file, int p_total, const Vector<String> &p_enc_in_filters, const Vector<String> &p_enc_ex_filters, const Vector<uint8_t> &p_key) {
	return OK;
}
Error EditorExportPlatformAndroid::copy_gradle_so(void *p_userdata, const SharedObject &p_so) {
	ERR_FAIL_COND_V_MSG(!p_so.path.get_file().begins_with("lib"), FAILED,
			"Android .so file names must start with \"lib\", but got: " + p_so.path);
	Vector<ABI> abis = get_abis();
	CustomExportData *export_data = static_cast<CustomExportData *>(p_userdata);
	bool exported = false;