Release 6.0.0-pre.20211202.4 (2021-12-20)

Baseline: 00a3354

Cherry picks:

   + c873525:
     Extract out constant for "current time" magic value in
     Path#setLastModifiedTime, to avoid confusion.
   + 7074bcf:
     Automated rollback of commit
     ed825a4.

Important changes:

  - alias() can now select() directly on constraint_value()

This release contains contributions from many people at Google, as well as Brentley Jones, Chris Fredrickson, Danny Wolf, Dimi Shahbaz, Ed Schouten, Fabian Meumertzheim, Fredrik Medley, Greg Estren, hvadehra, Noa Resare, Simon Bjorklen, Tetsuo Kiso.