bpo-32947: Fixes for TLS 1.3 and OpenSSL 1.1.1 (GH-8761)

bpo-32947: Fixes for TLS 1.3 and OpenSSL 1.1.1 (GH-8761)

Backport of TLS 1.3 related fixes from 3.7.

Misc fixes and workarounds for compatibility with OpenSSL 1.1.1 from git
master and TLS 1.3 support. With OpenSSL 1.1.1, Python negotiates TLS 1.3 by
default. Some test cases only apply to TLS 1.2.

OpenSSL 1.1.1 has added a new option OP_ENABLE_MIDDLEBOX_COMPAT for TLS
1.3. The feature is enabled by default for maximum compatibility with
broken middle boxes. Users should be able to disable the hack and CPython's test suite needs
it to verify default options

Signed-off-by: Christian Heimes <christian@python.org>