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
7 files changed