It also means that all supported OpenSSL versions and forks support
TLSv1.3 after this patch.

It reduces openssl.c size by more than 10%, or 400 LOC.

Ref: #18822

• align with deprecation plan and bump minimum to 3.0.0.
• old-linux relies on 1.0.2 support → try moving to GnuTLS, also needs fixing GnuTLS backend for that old (but supported) version → gnutls: fix building with older supported GnuTLS versions #18335
• Slackware 15.0 (in CI) requires 1.1.0. → disable SSL
• MS-DOS DJGPP also requires 1.0.2. It's an option to drop it completely or build without TLS. → GHA/non-native: drop MS-DOS jobs, requires OpenSSL 1.0.2 #18338
• bump to 3?
• fix typo in OpenSSL 1.1.1 check. (early data) → openssl: drop redundant version check #18333
• stop using OpenSSL 1.1.0 in AppVeyor CI → appveyor: drop testing with OpenSSL 1.1.0 #18341
• rebase on openssl: add and use HAVE_BORINGSSL_LIKE internal macro #18358 openssl: drop more legacy cruft #18359 openssl: add and use HAVE_OPENSSL3 internal macro #18360
• rebase on openssl: drop redundant HAVE_OPENSSL_VERSION macro #18367, drop pre-OpenSSL 3 non-fork logic.
• rebase on openssl: merge two #if blocks #18370.