Move kernel baseline tests to front_end.

pkg/front_end/testcases/casts.dart.direct.expect

 library;
 import self as self;
 import "dart:core" as core;
 
 static method main() → dynamic {
   core::print("" as core::String);
   core::print(1 as core::int);
   core::print(1.0 as core::double);
   core::print("" is core::String);
   core::print("" is core::int);
   core::print("" is core::double);
   core::print(1 is core::String);
   core::print(1 is core::int);
   core::print(1 is core::double);
   core::print(1.0 is core::String);
   core::print(1.0 is core::int);
   core::print(1.0 is core::double);
 }