0cc053b836
When setting up the paths to assets and ICU data, we were previously returning the underlying char* data in a temporary string returned by `std::filesystem::path::string()`. Since the return value of `string()` is never stored, there's no guarantee that the underlying data pointer is still valid later in the function. By storing the string in a local whose lifetime exceeds that of the running engine instance, we guarantee the string isn't freed until after the Flutter app terminates. [C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style