GitLab

Also introduce a build number in the package name, stop versioning
the Blink GC plugin, and remove repackage.sh.

BUG=444089
TBR=jln, jbauman
NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/975503002

Cr-Commit-Position: refs/heads/master@{#318797}