[remoting][FTL] Implement FtlDeviceIdProviderIos

This CL provides an FtlDeviceIdProvider implementation for the iOS
client, which generates the device ID from identifierForVendor:

https://developer.apple.com/documentation/uikit/uidevice/1620059-identifierforvendor?language=objc

Bug: 954594
Change-Id: Ieb5c373d66d17751294754c1674e86b8c7cb4ed3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1575116
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652671}
3 files changed