Sync of libtextclassifier from Google3.

Exported by: knowledge/cerebra/sense/text_classifier/lib/export_to_aosp.sh

Bug: 67618889
Test: Builds. Tested also with oc-mr1 and tested that smartselect/sharing features work.
Change-Id: I25ad82cdd5eed20c60e83e7eb94dae6ab08b3690