[lib] rename getForeignPeerDevices -> getForeignPeerDeviceIDs

Summary:
we only return the device IDs from this function, so renaming to make that more clear

Addressing feedback left in D12809

Depends on D12809

Test Plan: rename, so just ran flow

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13035