[yarn] Rename yarn patch to yarn arcpatch

Summary: Addresses point made by @tomek here: https://phab.comm.dev/D5445#inline-35863

Test Plan: Continues to work as expected... straightforward rename

Reviewers: varun, tomek, ginsu

Reviewed By: varun

Subscribers: ashoat, abosh, tomek

Differential Revision: https://phab.comm.dev/D5455