PT <-> TF for composite models
# What does this PR do?

Make `from_pretrained` (cross loading PT/TF) available for composite models. Ensure `enc_to_dec_proj` layer is correctly loaded.

With this PR, we can get the PT/TF same output for the test in #19719

I will apply the same change to Text and Speech composite models if the current version is approved.
_The documentation is not available anymore as the PR was closed or merged._