### 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
err += "\n";
			valid = false;
		}
		
		Ref<DirAccess> build_tools_da = DirAccess::open(sdk_path.path_join("build-tools"), &errn);
		if (errn != OK) {
			err += TTR("Invalid Android SDK path in Editor Settings.");
			err += TTR("Missing 'build-tools' directory!");
			err += "\n";
			valid = false;
		}
		String target_sdk_version = p_preset->get("custom_build/target_sdk");
		if (!target_sdk_version.is_valid_int()) {
			target_sdk_version = itos(DEFAULT_TARGET_SDK_VERSION);
		}
		
		String apksigner_path = get_apksigner_path(target_sdk_version.to_int());
		if (!FileAccess::exists(apksigner_path)) {
			err += TTR("Unable to find Android SDK build-tools' apksigner command.");
			err += TTR("Please check in the Android SDK directory specified in Editor Settings.");
			err += "\n";
			valid = false;
		}
	}
	if (!err.is_empty()) {
		r_error = err;
	}
	return valid;
}
bool EditorExportPlatformAndroid::has_valid_project_configuration(const Ref<EditorExportPreset> &p_preset, String &r_error) const {