Resolve the given id to file paths.
@param {boolean} isModule The flag which indicates this id is a module.
@param {string} id The id to resolve.
@param {object} options The options of node-resolve module.
It requires `options.basedir`.
@returns {string|null} The resolved path.
function getFilePath(isModule, id, options) {
    try {
        return resolve.sync(id, options)
    } catch (_err) {
        if (isModule) {
            return null
        }
        return path.resolve(options.basedir, id)
    }
}