[native] Fix appearance of TabNavigator in light mode
Summary:
Context: https://linear.app/comm/issue/ENG-2052/re-introduce-light-mode-in-native
The backgroundColor of TabNavigator was previously hardcoded to a dark value that looked fine in dark mode but looked broken in light mode.
This diff sets the backgroundColor to tabBarBackground which will adapt based on the theme.
Test Plan:
Before:
After:
Things look as expected.
Reviewers: tomek, marcin, ginsu, rohan, abosh, varun, O2 Blocking Reviewers, ashoat
Reviewed By: ginsu, O2 Blocking Reviewers, ashoat
Subscribers: ashoat
Differential Revision: https://phab.comm.dev/D5611