Function safe_app::ffi::mutable_data::permissions::mdata_permissions_get

#[no_mangle]
pub unsafe extern "C" fn mdata_permissions_get(
    app: *const App, 
    permissions_h: MDataPermissionsHandle, 
    user_h: SignPubKeyHandle, 
    user_data: *mut c_void, 
    o_cb: extern "C" fn(user_data: *mut c_void, result: *const FfiResult, perm_set: *const PermissionSet)
)

Get the permission set corresponding to the given user.

User is either handle to a signing key or USER_ANYONE.