Split "playback/exoplayer" Gradle module into two (#3781)

* Split media3-session to own Gradle module

* Rename playback.exoplayer to playback.media3-exoplayer

* Use submodule for media3

settings.gradle.kts

@@ -7,8 +7,9 @@ include(":app")
 
 // Modules
 include(":playback:core")
-include(":playback:exoplayer")
 include(":playback:jellyfin")
+include(":playback:media3:exoplayer")
+include(":playback:media3:session")
 include(":preference")
 
 pluginManagement {