The goal is to unify the high level control flow in entry points by
making them use a shared base class. Eventually, this will allow
us to test all aspects of request handling, including response
headers and output buffer handling. That will however require
us to move quite a bit of logic from ApiMain into ApiEntryPoint.
Bug: T354216
Change-Id: I4ea1cbb8b2786c24deade7d5029d95fe0c2abc57
