Baseline: ea8b99cf2a5914c67e4bd7651d83df98912bb1ed

Cherry picks:

   + 107a54edcf75dc026cf643df82c13fe32a1eb043:
     Fix flag file regexp broken by
     https://github.com/bazelbuild/bazel/commit/cb2cd9fd2b65311da92777
     7c35939701add5b879.
   + 1e7127dec96b69b8cd5d332551f8798433d6057e:
     Reinstate legacy worker flag file behaviour when not using
     --experimental_worker_strict_flagfiles.

Incompatible changes:

  - Flag --experimental_local_memory_estimate removed.

This release contains contributions from many people at Google, as well as Fabian Meumertzheim, Tomas Volf, Yannic Bonenberger.