Fix a few files with no or unusual copyright headers.
Manually add copyright headers to the legacy testprotos, which will
(probably) never be regenerated.
Change-Id: Ifb52fa0eb59bf9d2de40b8df7e581a3c9731c883
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/220498
Reviewed-by: Joe Tsai <joetsai@google.com>
Rename build tag "proto1_legacy" -> "protolegacy"
to be consistent with the "protoreflect" tag.
Rename flag constant "Proto1Legacy" -> "ProtoLegacy" since
it covers more than simply proto1 legacy features.
For example, it covers alpha-features of proto3 that
were eventually removed from the final proto3 release.
Change-Id: I0f4fcbadd4b5a61c87645e2e5be11d187e59157c
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/189345
Reviewed-by: Damien Neil <dneil@google.com>