[lib] Write some tests for text-utils: pluralizeAndTrim(...)

Summary: Did pluralize(...) and trim(...) so might as well do pluralizeAndTrim(...)

Test Plan: Ran tests

Reviewers: def-au1t, palys-swm, yayabosh

Reviewed By: palys-swm, yayabosh

Subscribers: ashoat, Adrian

Differential Revision: https://phab.comm.dev/D4329