[Android] Rework multidex and enable multidex for unit_tests_apk. (RELAND 2)

this is a reland of https://codereview.chromium.org/1590243003/

BUG=272790
TBR=thakis@chromium.org,yfriedman@chromium.org,phajdan.jr@chromium.org

Review URL: https://codereview.chromium.org/1594653002

Cr-Commit-Position: refs/heads/master@{#369906}
17 files changed