[nfc][mlgo] Separate logger and training-mode model evaluator

This just shuffles implementations and declarations around. Now the
logger and the TF C API-based model evaluator are separate.

Differential Revision: https://reviews.llvm.org/D131116

GitOrigin-RevId: 0cb9746a7d85000fc7bbd8ac5d8557179ca4521c
10 files changed