Add sections on Clang-Repl and Xeus-CPP to the Interactive C++ page

[QuillPusher]

Sources:

• Xeus Cpp: links mentioned here should have sufficient info for a brief section: Xeus-CPP Blog Post or feature page after input from QuantStack #184
• Clang-Repl: Compiler Research Org's contributions are mentioned in the "Execution Results Handling" section on this page: https://clang.llvm.org/docs/ClangRepl.html#capture-execution-results

Destination Page:

• https://compiler-research.org/interactive_cpp