use google.golang.org/protobuf/proto to encode mvt tile

[iwpnd]

description

tegola still depends on github.com/golang/protobuf/proto, which has been deprecated in favor of google.golang.org/protobuf/proto.

Swapping the import alone doesn't work because the generated .pb.go types (e.g. vector_tile.Tile of go-spatial/geom) were produced by the old protoc-gen-go and only satisfy the old proto.Message interface. The new runtime expects protoreflect.ProtoMessage, which requires a ProtoReflect() method these types don't have.

• regenerate .pb.go files using protoc-gen-go from google.golang.org/protobuf/cmd/protoc-gen-go in go-spatial/geom
• replace all imports of github.com/golang/protobuf/proto with google.golang.org/protobuf/proto.
• possibly fix any call-site breakage from differences in the generated code

[ARolek]

@iwpnd thanks for writing this one up.