Move legacy session calls to a new thread

Issue: #2577
Test: add Thread.sleep(5000) to setMetadata(), app stays responsive

Author: nift4

libraries/session/src/main/java/androidx/media3/session/MediaSessionImpl.java

@@ -231,7 +231,6 @@ public MediaSessionImpl(
         new MediaSessionLegacyStub(
             /* session= */ thisRef,
             sessionUri,
-            applicationHandler,
             tokenExtras,
             playIfSuppressed,
             customLayout,
@@ -240,7 +239,7 @@ public MediaSessionImpl(
             connectionResult.availablePlayerCommands,
             sessionExtras);
 
-    Token platformToken = sessionLegacyStub.getSessionCompat().getSessionToken().getToken();
+    Token platformToken = sessionLegacyStub.getSessionToken().getToken();
     sessionToken =
         new SessionToken(
             Process.myUid(),
@@ -980,7 +979,7 @@ public void connectFromService(IMediaController caller, ControllerInfo controlle
 
   @SuppressWarnings("UnnecessarilyFullyQualified") // Avoiding confusion by just using "Token"
   public android.media.session.MediaSession.Token getPlatformToken() {
-    return sessionLegacyStub.getSessionCompat().getSessionToken().getToken();
+    return sessionLegacyStub.getSessionToken().getToken();
   }
 
   public void setLegacyControllerConnectionTimeoutMs(long timeoutMs) {
@@ -1049,8 +1048,7 @@ protected IBinder getLegacyBrowserServiceBinder() {
     MediaSessionServiceLegacyStub legacyStub;
     synchronized (lock) {
       if (browserServiceLegacyStub == null) {
-        browserServiceLegacyStub =
-            createLegacyBrowserService(sessionLegacyStub.getSessionCompat().getSessionToken());
+        browserServiceLegacyStub = createLegacyBrowserService(sessionLegacyStub.getSessionToken());
       }
       legacyStub = browserServiceLegacyStub;
     }
@@ -1460,7 +1458,7 @@ private void handleAvailablePlayerCommandsChanged(Player.Commands availableComma
         sessionLegacyStub.onSkipToNext();
         return true;
       } else if (callerInfo.getControllerVersion() != ControllerInfo.LEGACY_CONTROLLER_VERSION) {
-        sessionLegacyStub.getSessionCompat().getController().dispatchMediaButtonEvent(keyEvent);
+        sessionLegacyStub.getControllerCompat().dispatchMediaButtonEvent(keyEvent);
         return true;
       }
       // This is an unhandled framework event. Return false to let the framework resolve by calling