MIGRATED_TO_CORE.md

Migrated To TensorFlow Core

Function	Status	Last TFA Version	First TF Version	Relevant PRs
metrics.F1Score & metrics.FBetaScore	In Progress			TF-31818 & TFA-430
utils.register_keras_custom_object	In Progress			TFA-438
activations.gelu	Proposed			TFA-550