Revert "Revert "Import external/python/jinja into master""

This reverts commit 81aec74062b5c629b3408f7f3d18343ec0bbcab8.

Reason for revert: It seems Jinja folder is empty. Revert the revert to add files back.

Third-party review: ag/11821018
Change-Id: I4429a3b3448cdf2eb62ec388392a2a29fa3dbc21
106 files changed