Replace REPL signal handling with raw mode jline terminal to make Ctrl-C handling work when REPL is a child process

[lihaoyi]

Rather than using JVM signal handling to trap the Ctrl-C, we instead make JLine set the terminal to raw mode and handle the Ctrl-C as a standard input character.

This is similar to what Ammonite (link) and (I think) JShell does, and has the advantage that it works even for stdin/stdout terminals inherited from parent processes (e.g. Mill or SBT) v.s. the current signal handling that only works when the REPL process is receiving the Ctrl-C directly.

Fixes com-lihaoyi/mill#6452 downstream in Mill, tested manually by cherry picking onto release-3.8.0, publishing locally, and using it in Mill

sbt --client scala3-compiler-bootstrapped-new/publishLocalBin &&
sbt --client scala-library-bootstrapped/publishLocalBin &&
sbt --client scala3-library-bootstrapped-new/publishLocalBin &&
sbt --client tasty-core-bootstrapped-new/publishLocalBin &&
sbt --client scala3-repl/publishLocalBin &&
sbt --client scala3-interfaces/publishLocalBin &&
sbt --client scala3-sbt-bridge-bootstrapped/publishLocalBin