Per discussion, we are changing the interpretation of a missing min sdk constraint (either because the constraint has no lower bound or because there is no constraint at all) as implying language version 2.7 instead of the latest language version. I believe that there is at least one tool in flutter which derives this to produce a package_config.json, and hence must be updated.

This is blocker for beta, and will need to be cherry picked if it doesn't make the beta branch cut.

cc @pcsosinski @mit-mit @franklinyow

cc @jonahwilliams @amirh @zanderso @jakemac53 @natebosch