This version adds signature algorithms to the extension
Change-Id: I91dc78d33ee81cb7a6221c7bdeefc8ea460a2d6c
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/42424
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>