crypto/tls: implement Extended Master Secret

crypto/tls: implement Extended Master Secret

All OpenSSL tests now test operation with EMS. To test a handshake
*without* EMS we need to pass -Options=-ExtendedMasterSecret which is
only available in OpenSSL 3.1, which breaks a number of other tests.

Updates #43922

Change-Id: Ib9ac79a1d03fab6bfba5fe9cd66689cff661cda7
Reviewed-on: https://go-review.googlesource.com/c/go/+/497376
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Damien Neil <dneil@google.com>