Rename WindowlessViewRoot to SurfaceControlViewHost and rework API

Should be a little more clear. The internal IWindowSession implementation
keeps the WindowlessWindowManager name, but the API section definitely
needs a more usable name. Instead of passing in a root Surface we want it
to be owned by the SurfaceControlViewHost itself. This way we can ensure
we only return a SurfacePackage. In follow up CLs we will add an
accessibility ID to the SurfacePackage so we can ensure the Control
is passed around with the accessibility ID.

Test: Builds
Bug: 134365580
Change-Id: I30520e8b169d3744a66ccedf61cc4515cfef4dee