Update some UI in PhotoPicker

- Adjust the height of the add button on the bottom bar
- Remove the gradients and set solid color to toolbar and bottom bar
  on the Preview tab in the Portrait mode.
- Update the height of the bottom bar on the preview tab

Test: video and screenshot on the bug
Test: atest PreviewSingleSelectTest
Bug: 204312505
Bug: 204743889
Change-Id: I30ca264b9a63fc8c6eefdddc058381b3b2b26956
diff --git a/res/values/colors.xml b/res/values/colors.xml
index 2337f98..1be725e 100644
--- a/res/values/colors.xml
+++ b/res/values/colors.xml
@@ -34,6 +34,7 @@
     <color name="picker_item_gradient_color">#42000000</color>
     <color name="preview_gradient_color_light">@android:color/transparent</color>
     <color name="preview_gradient_color_dark">#80202124</color>
+    <color name="preview_scrim_solid_color">#E6000000</color> <!-- 90% opacity black -->
 
     <!-- PhotoPicker Preview -->
     <color name="preview_default_blue">#8AB4F8</color>