PlayerService: Convert to kotlin (mechanical)

No adjustments done yet; only change is that I added an upper bound
on `PlayerUi` to the `PlayerUiList` functions, so “everything” is now
`null` in `destroyAll`.

Author: Profpatsch

app/src/main/java/org/schabi/newpipe/player/Player.java

@@ -481,15 +481,15 @@ private void initUIsForCurrentPlayerType() {
 
         switch (playerType) {
             case MAIN:
-                UIs.destroyAll(PopupPlayerUi.class);
+                UIs.destroyAllOfType(PopupPlayerUi.class);
                 UIs.addAndPrepare(new MainPlayerUi(this, binding));
                 break;
             case POPUP:
-                UIs.destroyAll(MainPlayerUi.class);
+                UIs.destroyAllOfType(MainPlayerUi.class);
                 UIs.addAndPrepare(new PopupPlayerUi(this, binding));
                 break;
             case AUDIO:
-                UIs.destroyAll(VideoPlayerUi.class);
+                UIs.destroyAllOfType(VideoPlayerUi.class);
                 break;
         }
     }
@@ -595,7 +595,7 @@ public void destroy() {
         databaseUpdateDisposable.clear();
         progressUpdateDisposable.set(null);
 
-        UIs.destroyAll(Object.class); // destroy every UI: obviously every UI extends Object
+        UIs.destroyAllOfType(null);
     }
 
     public void setRecovery() {
@@ -1971,6 +1971,9 @@ public void setFragmentListener(final PlayerServiceEventListener listener) {
         triggerProgressUpdate();
     }
 
+    /** Remove the listener, if it was set.
+     * @param listener listener to remove
+     * */
     public void removeFragmentListener(final PlayerServiceEventListener listener) {
         if (fragmentListener == listener) {
             fragmentListener = null;
@@ -1985,6 +1988,9 @@ void setActivityListener(final PlayerEventListener listener) {
         triggerProgressUpdate();
     }
 
+    /** Remove the listener, if it was set.
+     * @param listener listener to remove
+     * */
     void removeActivityListener(final PlayerEventListener listener) {
         if (activityListener == listener) {
             activityListener = null;