SurfaceFlinger: Validate layers before casting.

Reinterpret casting random IBinder = no-fun. I first attempted
to use inheritance of "getInterfaceDescriptor" in Layer::Handle but
departing from "standard-layout" (e.g. using virtual methods) means that
downcasting with static/reinterpret_cast is no longer valid. Instead I opted
for the pattern the system-server uses of maintaing a map.

Now that we look up the handle in a map rather than casting IBinder
to Layer::Handle we need to make sure we have unique instances of the
handle. In general this is true but we weren't doing this in the
createWithSurfaceParent where we had an extra call to getHandle. Here
we both refactor createWithSurfaceParent so it works with the new
changes and also add protection for getHandle. We also fix an error
where the handle map was populated outside of lock.

Bug: 129768960
Test: InvalidHandles_test.cpp ASurfaceControlTest SurfaceControlTest
Change-Id: I869bf6164c8d8203af7486ed1b12a763d5a56662