title: Your project has set `android.useAndroidX=true` but configuration `debugRuntimeClasspath` still contains legacy support libraries
body: <p>I am getting an warning in android studio when I run my app. the warning is-
  <em><strong>Your project has set <code>android.useAndroidX=true</code>, but configuration <code>debugRuntimeClasspath</code> still contains legacy support libraries, which may cause runtime issues.</strong></em>
  And a error-
  <em><strong>Manifest merger failed with multiple errors, see logs</strong></em>
  I checked my manifest file and there is no error in my manifest file. I tried debugging the app but it still doesn't fix. I am getting this after updating android studio from android studio arctic fox to android studio bumble bee which is recently released. I updated the gradle version tried cleaning project, invalidating caches but nothing worked. I increased the memory heap size and enabled multidex but still it is not fixed. Please help me out.</p>