Export textclassifier with downloader to sc-mainline-prod.

Gievn sc-mainline-prod is not merging to master now, will cherrypick
this to master manually.

Bug: 187927611
Bug: 186178939
Test: atest -p external/libtextclassifeir
Change-Id: I66fa477600ac5c2e221781bb3cb6416f64065b8f
174 files changed