title: what are the differences between MediaSessionCompat and MediaSession in android? and why there are androidx.media2 androidx.media both exists?
body: <p>I start new android app project with kotlin. my gradle configs for sdk are compileSdkVersion 29 and buildToolsVersion "29.0.1"</p>
  
  <p>I tried to make a feature which is remapping button of bluetooth earphone. So I found that I have to handle ACTION_MEDIA_BUTTON.</p>
  
  <p>It looks like <a href="https://developer.android.com/reference/kotlin/androidx/media2/session/MediaSession.html" rel="noreferrer">MediaSession</a> is later then <a href="https://developer.android.com/reference/kotlin/android/support/v4/media/session/MediaSessionCompat.html" rel="noreferrer">MediaSessionCompat</a>. But I don't know what should I use.</p>
  
  <p>About androidx. I wonder why they divided the package like androidx.media and androidx.media2?</p>