This GREASEs cipher suites, groups, and extensions. For now, we'll
always place them in a hard-coded position. We can experiment with more
interesting strategies later.

If we add new ciphers and curves, presumably we prefer them over current
ones, so place GREASE values at the front. This prevents implementations
from parsing only the first value and ignoring the rest.

Add two new extensions, one empty and one non-empty. Place the empty one
in front (IBM WebSphere can't handle trailing empty extensions) and the
non-empty one at the end.

Change-Id: If2e009936bc298cedf2a7a593ce7d5d5ddbb841a
Reviewed-on: https://boringssl-review.googlesource.com/11241
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>