protobuf: remove gogoproto

Removes gogo/protobuf from buildx and updates to a version of
moby/buildkit where gogo is removed.

This also changes how the proto files are generated. This is because
newer versions of protobuf are more strict about name conflicts. If two
files have the same name (even if they are relative paths) and are used
in different protoc commands, they'll conflict in the registry.

Since protobuf file generation doesn't work very well with
`paths=source_relative`, this removes the `go:generate` expression and
just relies on the dockerfile to perform the generation.

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

vendor/github.com/cespare/xxhash/v2/xxhash.go

@@ -19,10 +19,13 @@ const (
 // Store the primes in an array as well.
 //
 // The consts are used when possible in Go code to avoid MOVs but we need a
-// contiguous array of the assembly code.
+// contiguous array for the assembly code.
 var primes = [...]uint64{prime1, prime2, prime3, prime4, prime5}
 
 // Digest implements hash.Hash64.
+//
+// Note that a zero-valued Digest is not ready to receive writes.
+// Call Reset or create a Digest using New before calling other methods.
 type Digest struct {
 	v1    uint64
 	v2    uint64
@@ -33,19 +36,31 @@ type Digest struct {
 	n     int // how much of mem is used
 }
 
-// New creates a new Digest that computes the 64-bit xxHash algorithm.
+// New creates a new Digest with a zero seed.
 func New() *Digest {
+	return NewWithSeed(0)
+}
+
+// NewWithSeed creates a new Digest with the given seed.
+func NewWithSeed(seed uint64) *Digest {
 	var d Digest
-	d.Reset()
+	d.ResetWithSeed(seed)
 	return &d
 }
 
 // Reset clears the Digest's state so that it can be reused.
+// It uses a seed value of zero.
 func (d *Digest) Reset() {
-	d.v1 = primes[0] + prime2
-	d.v2 = prime2
-	d.v3 = 0
-	d.v4 = -primes[0]
+	d.ResetWithSeed(0)
+}
+
+// ResetWithSeed clears the Digest's state so that it can be reused.
+// It uses the given seed to initialize the state.
+func (d *Digest) ResetWithSeed(seed uint64) {
+	d.v1 = seed + prime1 + prime2
+	d.v2 = seed + prime2
+	d.v3 = seed
+	d.v4 = seed - prime1
 	d.total = 0
 	d.n = 0
 }