group reparenting tests for view culling together (facebook#50886)

Summary:
Pull Request resolved: facebook#50886

changelog: [internal]

Group tests related to reparenting in "describe" block. Differentiator is two algorithms hidden behind a single interface: regular and reparenting. The tests are structured this way as well where regular tests focus on common scenarios and reparenting section focuses on reparenting and special cases around that. The reparenting implementation is considerably more complex as it handles edge cases that don't happen often.

Reviewed By: mdvacca

Differential Revision: D73541053

fbshipit-source-id: c3905a0f0117cb1aa6c468e24e6bb982de48545d

Author: sammy-SC