crypto/tls: FIPS 140-3 mode

Consolidates handling of FIPS 140-3 considerations for the tls package.
Considerations specific to certificates are now handled in tls instead
of x509 to limit the area-of-effect of FIPS as much as possible.
Boringcrypto specific prefixes are renamed as appropriate.

For #69536

Co-authored-by: Filippo Valsorda <filippo@golang.org>
Change-Id: I1b1fef83c3599e4c9b98ad81db582ac93253030b
Reviewed-on: https://go-review.googlesource.com/c/go/+/629675
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

fipsonly/fipsonly_test.go

@@ -7,12 +7,12 @@
 package fipsonly
 
 import (
-	"crypto/internal/boring/fipstls"
+	"crypto/tls/internal/fips140tls"
 	"testing"
 )
 
 func Test(t *testing.T) {
-	if !fipstls.Required() {
-		t.Fatal("fipstls.Required() = false, must be true")
+	if !fips140tls.Required() {
+		t.Fatal("fips140tls.Required() = false, must be true")
 	}
 }