[native] Allow MediaGallery items to mount pre-selected

Summary:
For the approach described in https://linear.app/comm/issue/ENG-2411#comment-c4d6a4a4 to work, items can appear in MediaGalleryKeyboard preselected.
I need that MediaGalleryMedia component can be mounted with the pre-selected state already.

I basically copied code that animates the green checkmark from componentDidUpdate to componentDidMount.

Test Plan: Ensured that items that have isQueued = true when mounted have the green checkmark displayed and animated.

Reviewers: ashoat, przemek, inka, ginsu

Reviewed By: ashoat

Subscribers: tomek, atul

Differential Revision: https://phab.comm.dev/D6494