android: expose JitsiMeetActivity.leave()

android/sdk/src/main/java/org/jitsi/meet/sdk/JitsiMeetActivity.java

 
     @Override
     public void finish() {
-        getJitsiView().leave();
+        leave();
 
         super.finish();
     }
         getJitsiView().join(options);
     }
 
+    public void leave() {
+        getJitsiView().leave();
+    }
+
     private @Nullable JitsiMeetConferenceOptions getConferenceOptions(Intent intent) {
         String action = intent.getAction();