Maintenance: sync with upstream crypto/tls

[gaukas]

Sync with latest implementation from upstream crypto/tls and make some minor changes to fix the incompatibility.

Introduced new issues

• All test cases in TestUTLSHandshakeClientParrotGolang has failed.
  • It is possibly OK, since crypto/tls has been modified heavily and we won't expect to see the server response to be the same as 4 years ago.
  • The failing tests are now disabled. But contributors are welcome to fix these tests.

Persistent issues

• The forgeConn() in the example in examples folder is broken, since the cipher suite checking in tls.MakeConnWithCompleteHandshake() doesn't work with TLS 1.3.

[gaukas]

Possibly want to get this merged fast, before any merge conflict arises.

[gaukas]

Will provide an alternative version with 2 commits: one for sync up and one for modifications needed for compatibility.

[gaukas]

See #120 instead.