[Clang-Repl] Add support for out-of-process execution. (#110418)

This PR introduces out-of-process (OOP) execution support for
Clang-Repl. With this enhancement, two new flags, `oop-executor` and
`oop-executor-connect`, are added to the Clang-Repl interface. These
flags enable the launch of an external executor
(`llvm-jitlink-executor`), which handles code execution in a separate
process.