Refactor codes for AlbumsTabFragment

- Extract the TabFragment
- Rename BaseItemHolder to BaseViewHolder
- Modify the onItemClick for single select in PhotosTabFragment
  Add clearSelectedItems in PickerViewModel
- Add PhotosTabItemDecoration to adjust the gap of RecyclerView
- Support dark theme on date header
- Change the position of the check icon and the badges in RTL

Test: atest PickerViewModelTest
Test: screenshot on b/191746644
Bug: 191746644
Bug: 191127346
Bug: 191937323
Change-Id: Ie099a56104d7ee2f00acfac4566e898f4e2d8b29
Merged-In: Ie099a56104d7ee2f00acfac4566e898f4e2d8b29
(cherry picked from commit 34652dc00e7e2e917190a206530384f1a6d9e07f)
diff --git a/res/values/dimens.xml b/res/values/dimens.xml
index 28a7b60..cee0809 100644
--- a/res/values/dimens.xml
+++ b/res/values/dimens.xml
@@ -22,18 +22,23 @@
 
     <!-- PhotoPicker -->
     <dimen name="picker_photo_size">118dp</dimen>
+
     <dimen name="picker_bottom_bar_size">56dp</dimen>
     <dimen name="picker_bottom_bar_horizontal_gap">16dp</dimen>
     <dimen name="picker_bottom_bar_vertical_gap">10dp</dimen>
     <dimen name="picker_bottom_bar_elevation">8dp</dimen>
+
     <dimen name="picker_item_check_size">24dp</dimen>
     <dimen name="picker_item_check_margin">6dp</dimen>
     <dimen name="picker_item_badge_margin">5dp</dimen>
     <dimen name="picker_item_badge_text_margin">3dp</dimen>
     <dimen name="picker_item_badge_text_size">10dp</dimen>
+
     <dimen name="picker_date_header_height">56dp</dimen>
     <dimen name="picker_date_header_padding">16dp</dimen>
 
+    <dimen name="picker_photo_item_spacing">3dp</dimen>
+
     <!-- PhotoPicker Preview -->
     <dimen name="preview_buttons_margin_horizontal">16dp</dimen>
     <dimen name="preview_buttons_margin_bottom">10dp</dimen>