[QuickStart] Add scaffolding code for TargetFidoController

This CL adds the basic constructors and structure of the
TargetFidoController class which will handle packing the GetAssertion
request and transporting it via NearbyConnections to Android.

Bug: b/236756892
Change-Id: I0e56a0023f9ba2a275c5326163cc47bd08046559
Tested: Added unit test fixtures for barebones TargetFidoController
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3749348
Commit-Queue: Jason Rhee <jasonrhee@google.com>
Reviewed-by: Michael Hansen <hansenmichael@google.com>
Cr-Commit-Position: refs/heads/main@{#1024433}