[lib] modified stringForReactionList to handle more than 9 likes/reactions for the same reaction type

Summary:
modified stringForReactionList to handle more than 9 likes/reactions for the same reaction type. Made the decision to cap the number of likes at 9, and then everything after will display 9+. If we want to change this though to another number, please let me know This was suggested by @atul in D5953

Depends on D5953

Test Plan:
ran yarn test reaction-utils.test.js with a new unit test that has 12 message likes and all tests passed

Reviewers: atul, tomek

Reviewed By: atul, tomek

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D5974