[profi][NFC] Get rid of afdo_detail::TypeMap

Parametrize SampleProfileInference and SampleProfileLoaderBaseImpl by function
type (Function/MachineFunction) instead of block type
(BasicBlock/MachineBasicBlock). Move out specializations to appropriate
locations.

This change makes it possible to use GraphTraits instead of a custom TypeMap and
make SampleProfileInference not dependent on LLVM types, paving the way for
generalizing SampleProfileInference interfaces to BOLT IR types
(BinaryFunction/BinaryBasicBlock) in stale profile matching (D144500).

Reviewed By: hoy

Differential Revision: https://reviews.llvm.org/D152187