Add a setting/API to run a code snippet/script in the REPL on startup

[Gedochao]

What needs to be done

We need a way to pass a code snippet or Scala source file that'd be run on REPL startup.
This is very similar to Ammonite REPL's (https://github.com/com-lihaoyi/Ammonite or --amm passed to Scala CLI) -c/--code option.

Why do we need this?

• it'd make REPL integrations testable on Scala CLI's side (things like Fix the REPL crashing when a dependency's classpath is called by a macro VirtusLab/scala-cli#3043 (comment))
• it'd enable working around package wildcard exports discussed in Support for initial commands in REPL VirtusLab/scala-cli#604

Requirements

I'd imagine we need:

• a way to pass a code snippet or source file to the REPL main class to be executed at REPL startup
  • something like this:

  java
  -Dscala.usejavacp=true
  -classpath (...)
  dotty.tools.repl.Main
  -classpath (...)
  --init-script 'println("Hello from the init script in REPL")'
  # Welcome to Scala 3.4.2 (17, Java OpenJDK 64-Bit Server VM).
  # Type in expressions for evaluation. Or try :help.
  # 
  # Hello from the init script in REPL
  # scala> 

• a way to skip the interactive mode and execute the script inside of the REPL, similar to what the -e flag does outside of the REPL
  • this would make testing integrations a lot easier
  • Ammonite equivalent:

  scala-cli repl --power --amm --ammonite-arg -c --ammonite-arg 'println("Hello from the init script in REPL")'
  # Compiling ~/Downloads/(console)
  # Hello from the init script in REPL

Context

Past discussions:

• Support for initial commands in REPL VirtusLab/scala-cli#604
• --interactive should not close the terminal after piping Scala code VirtusLab/scala-cli#2185
• Feature initImportREPL: allow initial imports to be automatically available in repl session  VirtusLab/scala-cli#2732
• https://users.scala-lang.org/t/load-a-file-on-startup-into-scala-3-repl/9943/10

[noti0na1]

The second point will be implemented in a separate PR.