Export more APIs through the expect library (#213)

When we split `test_api` into smaller libraries I did not include some
deprecated or less used APIs through the "focused" library
`expect.dart`, while still exporting them through the combined
`test_api.dart` library to avoid a backwards incompatibility.

Now that we are moving the APIs to a package we will discontinue, it is
not as valuable to try to push migrations between APIs _within_ the
package, so re-export them through the `expect.dart` library. This
reduces the level of breaking change so that an import update will be
all that is needed in every case.
diff --git a/lib/expect.dart b/lib/expect.dart
index d790b7c..c842d30 100644
--- a/lib/expect.dart
+++ b/lib/expect.dart
@@ -6,7 +6,7 @@
 
 export 'matcher.dart';
 
-export 'src/expect/expect.dart' show expect, expectLater, fail;
+export 'src/expect/expect.dart' show ErrorFormatter, expect, expectLater, fail;
 export 'src/expect/expect_async.dart'
     show
         Func0,
@@ -48,7 +48,7 @@
         emitsThrough,
         mayEmitMultiple,
         neverEmits;
-export 'src/expect/throws_matcher.dart' show throwsA;
+export 'src/expect/throws_matcher.dart' show Throws, throws, throwsA;
 export 'src/expect/throws_matchers.dart'
     show
         throwsArgumentError,