Summary:
This diff upgrades xplat to 0.178.1 and pre-suppresses errors from turning on constrained writes.
To generate this diff I:
* Modified every `env_mode=constrain_writes` to `env_mode=ssa` and made a commit (this is so our upgrade script will work)
* Ran scripts/flow/upgrade.sh 0.178.1 to upgrade all the flowconfigs to 178.1 and suppress new-env errors
* Modified arvr/js/flowconfig.ejs to use 0.178.1 and ran `scripts/gen-flowconfig/gen-flowconfig --project arvr`
* Modified xplat/js/flowconfig.ejs to use 0.178.1 and ran `scripts/gen-flowconfig/gen-flowconfig --project xplat`
* Unstacked from the commit in point 1
Reviewed By: SamChou19815
Differential Revision: D36676019
fbshipit-source-id: c3032f18ed838afc327f00de563e7f20713bdc26
6064fd0600