Baseline: 5767cba4044c2bfd8a4c9596c44d2363630b489d

Incompatible changes:

  - Added a new flag
    --incompatible_unambiguous_label_stringification, which causes
    labels in the main repo to stringify into unambiguous forms
    starting with an @. See
    https://github.com/bazelbuild/bazel/issues/15916 for more
    information.

This release contains contributions from many people at Google, as well as Philipp Schrader.