[native] Fix invite link button positioning

Summary:
The button was positioned incorrectly and was overlapping with long community name. Also, community name could fill the whole available space.

Test Plan: Check if the button is displayed correctly even when the name is long.

Reviewers: bartek, kamil, inka, ted

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D8204