Implement "pause/play" toggle on hardware keyboard space button.

app/src/main/java/org/schabi/newpipe/fragments/detail/VideoDetailFragment.java

@@ -1850,6 +1850,7 @@ public final class VideoDetailFragment
 
         if (fullscreen) {
             hideSystemUiIfNeeded();
+            binding.overlayPlayPauseButton.requestFocus();
         } else {
             showSystemUi();
         }

app/src/main/res/layout/fragment_video_detail.xml

@@ -675,6 +675,8 @@
                 android:background="?attr/selectableItemBackground"
                 android:padding="10dp"
                 android:scaleType="center"
+                android:focusable="true"
+                android:focusedByDefault="true"
                 app:srcCompat="?attr/ic_play_arrow"
                 tools:ignore="ContentDescription,RtlHardcoded" />