Bump to the Android Gradle Plugin 4.0.1

This additionally adds the `android.useAndroidX` option
to fix an error raised by the new plugin. Note that this
might potentially fix bug 1645372.

build.gradle

@@ -11,7 +11,7 @@ buildscript {
     // changing them. Please note that, for using in Android-Components, the
     // versions below must match the ones in that repository.
     ext.versions = [
-        android_gradle_plugin: '3.5.3',
+        android_gradle_plugin: '4.0.1',
         android_maven_publish_plugin: '3.6.2',
         coroutines: '1.3.5',
         dokka: '0.9.17',

gradle.properties

@@ -21,3 +21,5 @@ libVcsUrl=https://github.com/mozilla/glean.git
 
 libLicense=MPL-2.0
 libLicenseUrl=https://www.mozilla.org/en-US/MPL/2.0/
+
+android.useAndroidX=true