Allow conditioning flags on the _absence_ of a feature.

This allows a flag_set to emit one flag when a feature is enabled, and a
different flag when that feature is disabled.

And while I was in there, I noticed and fixed a couple other issues:

1. env_set didn't actually implement with_feature, despite having the field in
   its proto.
2. action_config implemented with_feature as an optional field, instead of
   repeated field.

RELNOTES: None
PiperOrigin-RevId: 176510960
1 file changed
tree: 46c1af864dd5b88b531d49db98e8c2f8b0edc6c6
  1. third_party/