[native] update avatar size variants to use t-shirt sizes

Summary:
For the user profile avatar view, I plan to introduce a new avatar size. In D8913, @atul called out switching the names of the avatar sizes from this generic/usage convention to a uniform naming convention. Figured before I introduce this new size, it would be worthwhile now to address this feedback

https://linear.app/comm/issue/ENG-4815/update-avatar-size-variants-to-use-t-shirt-sizes

Test Plan: flow and confirmed that there were no regressions with the avatar sizes

Reviewers: atul, inka

Reviewed By: atul

Subscribers: ashoat, tomek, wyilio, atul

Differential Revision: https://phab.comm.dev/D9364