security/s2n-tls: Various improvements

• Define LICENSE_FILE
• Use ports framework for unit testing
• Add option for assembly optimization and LTO
• Disable building tests by default
• Disable assembly optimization by default (requires AVX2 and BMI2 support without runtime detection)
• Use CMake helpers provided by framework
• Rename s2n -> s2n-tls to match upstream name

PR: 266397