This change adds the first Go specific editions feature and the
associated proto. The feature is used to control if the legacy
UnmarshalJSON method should be generated for enums. This change only
affects protos using editions.
More tests will be added in a followup change.
Change-Id: Ifb62454d7568bd6d90d0b93f8953adcfe46c45fd
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/561938
Reviewed-by: Michael Stapelberg <stapelberg@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Lasse Folger <lassefolger@google.com>