[go1.16] bump golang.org/x/... dependencies

hack/pin-dependency.sh golang.org/x/crypto latest
hack/pin-dependency.sh golang.org/x/net latest
hack/pin-dependency.sh golang.org/x/exp latest
hack/pin-dependency.sh golang.org/x/sys latest
hack/pin-dependency.sh golang.org/x/time latest
hack/pin-dependency.sh golang.org/x/tools latest

hack/lint-dependencies.sh
hack/pin-dependency.sh dmitri.shuralyov.com/gpu/mtl v0.0.0-20201218220906-28db891af037
hack/pin-dependency.sh golang.org/x/mobile v0.0.0-20201217150744-e6ae53a27f4f
hack/pin-dependency.sh golang.org/x/mod v0.3.1-0.20200828183125-ce943fd02449

hack/lint-dependencies.sh

hack/update-internal-modules.sh
hack/update-vendor.sh

Co-authored-by: Stephen Augustus <foo@auggie.dev>

vendor/golang.org/x/sys/plan9/str.go

@@ -0,0 +1,22 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build plan9
+
+package plan9
+
+func itoa(val int) string { // do it here rather than with fmt to avoid dependency
+	if val < 0 {
+		return "-" + itoa(-val)
+	}
+	var buf [32]byte // big enough for int64
+	i := len(buf) - 1
+	for val >= 10 {
+		buf[i] = byte(val%10 + '0')
+		i--
+		val /= 10
+	}
+	buf[i] = byte(val + '0')
+	return string(buf[i:])
+}