Add package:ffi as path dependency to flutter_frontend_server (#37802)
Add package:ffi as path dependency to flutter_frontend_server (#37802)

The CL in [0] added package:ffi as dependency to package:compiler. Since
flutter_frontend_server needs all dependencies as path dependencies, we
need to add package:ffi there via path.

[0] https://dart-review.googlesource.com/c/sdk/+/269640
flutter/engine,flutter/engine,flutter/engine,flutter/engine,flutter/engine,flutter/engine,flutter/engine,flutter/engine