This separates the reading of entry-points, which do not have an
accessor library, from reading of imports, exports and parts, which must
have an access library.
This change also disallows access to platform private libraries, like
dart:_internal, as entry-points.
Change-Id: I017ca30231eb99dc8463266dca0973a02f6f0e30
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/223423
Reviewed-by: Chloe Stefantsova <cstefantsova@google.com>
Johnni Winther
81ee883c98