Do not import top level library internally

Author: HosseinYousefi

pkgs/jni/lib/src/errors.dart

@@ -4,7 +4,8 @@
 
 import 'dart:io';
 
-import '../_internal.dart';
+import 'package:meta/meta.dart' show internal;
+
 import 'third_party/generated_bindings.dart';
 
 // TODO(#567): Add the fact that [JException] is now a [JObject] to the

pkgs/jni/lib/src/jimplementer.dart

@@ -5,12 +5,17 @@
 import 'dart:ffi';
 import 'dart:isolate';
 
+import 'package:ffi/ffi.dart';
 import 'package:meta/meta.dart' show internal;
 
-import '../jni.dart';
 import 'accessors.dart';
 import 'jni.dart';
+import 'jobject.dart';
+import 'jreference.dart';
+import 'lang/jstring.dart';
 import 'third_party/generated_bindings.dart';
+import 'types.dart';
+import 'util/jlist.dart';
 
 /// A builder that builds proxy objects that implement one or more interfaces.
 ///