Import libtextclassifier changes from google3.

This includes an upgrade to the latest version of the model.

We now use a test data path constant in the unit tests. This is
consistent with another test project, minikin_tests.

Test: Tests pass on-device.
Bug: 34865247
Change-Id: Ia061888a0bba371c6b429ad7c5457af611ba12f2
11 files changed