[Native] Encode platform type in native_rust_library

Summary:
Have the native_rust_library be aware of the
underlying platform to communicate that information
during registration of the device

https://linear.app/comm/issue/ENG-4608

Depends on D8749

Test Plan:
Android and iOS build
Can't be tested fully until native login if fully implmented.

Reviewers: bartek, varun, ashoat

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8816