[native] rename native themes-types to theme-utils
Summary:
Now that we lifted all the theme types into lib, the native file types would be better named as a utils file
Depends on D9528
Test Plan: flow and confirmed that updating the app theme on native still works as expected
Reviewers: atul, inka, rohan
Reviewed By: atul
Subscribers: ashoat, tomek, wyilio
Differential Revision: https://phab.comm.dev/D9529