[lib] Introduce getEntityTextAsString

Summary:
This diff builds on its parent (which introduces getENSNames) and introduces an async function that will resolve EntityText to a string, with ENS names swapped out.

This function along with useEntityTextAsString should replace most places we call entityTextToRawString today.

Depends on D6565

Test Plan: Tested in combination with following diffs, where it's actually used

Reviewers: atul

Reviewed By: atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D6566