[lib] Introduce decodeThreadRolePermissionsBitmaskArray

Summary:
Self explanatory, inverse of threadRolePermissionsBlobToBitmaskArray.

Depends on D9687

Test Plan: Unit test, will add more later w/ test data from my "prod" redux store.

Reviewers: ashoat, tomek, ginsu, rohan

Reviewed By: ashoat

Subscribers: wyilio

Differential Revision: https://phab.comm.dev/D9689