Add an FAQ on resolving SharedPartBuilder output (#2892)
Add an FAQ on resolving SharedPartBuilder output (#2892)

This has come up as a general question about builder ordering, and it
was difficult to realize that the reasoning was that it isn't resolvable
Dart code until after the `.g.dart` file is written. Add an FAQ entry to
make this more discoverable. For example #2701
dart-lang/build,dart-lang/build,dart-lang/build,dart-lang/build