Add .jinja2 extension to XML manifests that get preprocessed

These Android files get run through the jinja2 template processor
and the actually .xml files are created in the $OUT directory
during the build flow. So make it obvious that these files are
not XML.

Review URL: https://codereview.chromium.org/780973002

Cr-Commit-Position: refs/heads/master@{#306955}
12 files changed