Add Preview for single select

Added support for previewing selected item.

The CL supports
1. Previewing images only, doesn't support videos
2. Preview with basic layout and doesn't completely mirror UX mocks.
3. Preview for single select, doesn't support preview for multi select

Bug: 185801129
Test: Test video is added to the bug.
Change-Id: I1edbbff3cb6467e75a17243b70378e74c8d0968b
Merged-In: I1edbbff3cb6467e75a17243b70378e74c8d0968b
(cherry picked from commit 3e52acf12b01d64af5ff5873ae9600ae65c35f6a)
diff --git a/res/values/dimens.xml b/res/values/dimens.xml
index 4f1dbca..fb4cbbe 100644
--- a/res/values/dimens.xml
+++ b/res/values/dimens.xml
@@ -20,6 +20,11 @@
     <dimen name="permission_thumb_margin">6dp</dimen>
     <dimen name="dialog_space">20dp</dimen>
 
-    <!-- photo picker -->
+    <!-- PhotoPicker -->
     <dimen name="picker_photo_size">118dp</dimen>
+
+    <!-- PhotoPicker Preview -->
+    <dimen name="preview_buttons_margin_horizontal">16dp</dimen>
+    <dimen name="preview_buttons_margin_bottom">10dp</dimen>
+    <dimen name="preview_buttons_text_size">14sp</dimen>
 </resources>