Reduce the size of thumbnails on big screens to fit more grid columns

Reverts part of TeamNewPipe#9310, which introduced bigger grid thumbnail sizes on big screens, because some users reported not being happy about having too few grid columns. See TeamNewPipe#9310 (comment) .

Author: Stypox

app/src/main/res/values-w820dp/dimens.xml

@@ -4,6 +4,6 @@
          would include 7" and 10" devices in landscape (~960dp and ~1280dp respectively). -->
     <dimen name="activity_horizontal_margin">64dp</dimen>
 
-    <dimen name="video_item_grid_thumbnail_image_width">280dp</dimen>
-    <dimen name="video_item_grid_thumbnail_image_height">160dp</dimen>
+    <dimen name="video_item_grid_thumbnail_image_width">208dp</dimen>
+    <dimen name="video_item_grid_thumbnail_image_height">117dp</dimen>
 </resources>