[web] Replace threadHasPermission with useThreadHasPermission in MembersModal

Summary:
Similar to D11751, but for MembersModal.

Depends on D11751

Test Plan:
flow + close reading.

Will test generally at end to make sure things work as expected. Don't think it's practical to manually test each of these trivial changes.

Reviewers: varun, ginsu, tomek, will

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11752