[native] Add fontSize option to Pill and ThreadPill components

Summary:
Adding the possibility to change font size in Pill/ThreadPill components, because I'll need that in subchannels/sidebars modals, as discussed in
https://linear.app/comm/issue/ENG-2547/restyle-sidebarlistmodal-and-subchannelslistmodal

Test Plan: Run ios simulator, check that pills display correctly - ex in chat settings. Check that passing a fontSize prop changes the fon size.

Reviewers: przemek, bartek, kamil, tomek

Reviewed By: bartek, tomek

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D6259