Small Transformer refactor: combine line/lineSegment
Small Transformer refactor: combine line/lineSegment

Test Plan: none

Auditors: alex

iamchenxin/perseus,ariabuckles/perseus,iamchenxin/perseus,learningequality/perseus,sachgits/perseus,ariabuckles/perseus,junyiacademy/perseus,alexristich/perseus,ariabuckles/perseus,daukantas/perseus,chirilo/perseus,huangins/perseus,abe4mvp/perseus,alexristich/perseus,chirilo/perseus,huangins/perseus,abe4mvp/perseus,ariabuckles/perseus,sachgits/perseus,learningequality/perseus,daukantas/perseus,junyiacademy/perseus