This commit contains:
1. the C API headers (under tf/c/experimental/saved_model/public),
2. the C -> C++ implementation glue code (under tf/c/experimental/saved_model/internal)
3. the C++ implementation (under tf/c/experimental/saved_model/core)
The C++ implementation (3) is currently a stub.
Please note: The C++ header-only API wrapping the C API will be added in a subsequent change.
Certain aspects of this C API are expected to change heavily (mainly regarding ConcreteFunction execution).
PiperOrigin-RevId: 307419836
Change-Id: I6755fca97394d47c09799c534236ac17a30410d1