feat: upgrade gradle to 6.1 & gradle build tools to 3.5.3 (#792)

* feat!: upgrade gradle to 6.1
* feat!: upgrade gradle build tools to 3.5.3
* feat: added `npm run clean-tests`
* fix!: Removed useDeprecatedNdk as this option is now completely removed from gradle.
* feat!: bump gradle to 6.1 & gradle build tools to 3.5.3

Co-authored-by: エリス <erisu@users.noreply.github.com>

bin/clean_test.js

@@ -0,0 +1,28 @@
+/*
+       Licensed to the Apache Software Foundation (ASF) under one
+       or more contributor license agreements.  See the NOTICE file
+       distributed with this work for additional information
+       regarding copyright ownership.  The ASF licenses this file
+       to you under the Apache License, Version 2.0 (the
+       "License"); you may not use this file except in compliance
+       with the License.  You may obtain a copy of the License at
+
+         http://www.apache.org/licenses/LICENSE-2.0
+
+       Unless required by applicable law or agreed to in writing,
+       software distributed under the License is distributed on an
+       "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+       KIND, either express or implied.  See the License for the
+       specific language governing permissions and limitations
+       under the License.
+*/
+
+const fs = require('fs');
+
+if (fs.existsSync('./test/gradlew')) {
+    fs.unlinkSync('./test/gradlew');
+}
+
+if (fs.existsSync('./test/gradlew.bat')) {
+    fs.unlinkSync('./test/gradlew.bat');
+}