feat(reset): add binding and api method for git_reset_default (#14)

test/reset_test.dart

@@ -61,5 +61,32 @@ void main() {
 
       index.free();
     });
+
+    group('resetDefault', () {
+      test('successfully updates entry in the index', () {
+        file.writeAsStringSync('new edit');
+
+        final index = repo.index;
+        index.add('feature_file');
+        expect(repo.status['feature_file'], {GitStatus.indexModified});
+
+        final head = repo.head;
+        repo.resetDefault(oid: head.target, pathspec: ['feature_file']);
+        expect(repo.status['feature_file'], {GitStatus.wtModified});
+
+        head.free();
+        index.free();
+      });
+
+      test('throws when pathspec list is empty', () {
+        final head = repo.head;
+        expect(
+          () => repo.resetDefault(oid: head.target, pathspec: []),
+          throwsA(isA<LibGit2Error>()),
+        );
+
+        head.free();
+      });
+    });
   });
 }