This ensures different valid protobuf serializations that are sent by
frontends will be rewritten into digests that are normalized for the
buildkit solver.
The most recent example of this is that older frontends would generate
protobuf with gogo and the newer buildkit is using the google protobuf
library. These produce different serializations and cause the solver to
think that identical operations are actually different.
Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>
