Allow shading of single-choice compiler options from the command line regardless of -/-- prefix

[Gedochao]

Scala CLI allows (even before this PR) to override using directive settings from the command line, including single-choice (non-repeatable) compiler options.

Given a source file unused.scala:

//> using options -Wunused:all -Werror
@main def main() = {
  val unusedValue = "something"
  println("Hello, world!")
}

The unused warning produced by -Wunused:all would get raised to an error due to -Werror.

scala-cli compile unused.scala
# Compiling project (Scala 3.5.1, JVM (17))
# [warn] ./repro.scala:3:7
# [warn] unused local definition
# [warn]   val unusedValue = "something"
# [warn]       ^^^^^^^^^^^
# Error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
# Error compiling project (Scala 3.5.1, JVM (17))
# Compilation failed

However, -Werror can be overridden from the command line with -Werror:false, without editing sources:

scala-cli compile repro.scala -Werror:false                      
# Compiling project (Scala 3.5.1, JVM (17))
# [warn] ./repro.scala:3:7
# [warn] unused local definition
# [warn]   val unusedValue = "something"
# [warn]       ^^^^^^^^^^^
# Compiled project (Scala 3.5.1, JVM (17))

This PR allows to perform overriding like this regardless if the option key is preceded with a single - (-Werror) or double (--Werror).
So this allows for an override like:

scala-cli compile repro.scala --Werror:false                    
# Compiling project (Scala 3.5.1, JVM (17))
# [warn] ./repro.scala:3:7
# [warn] unused local definition
# [warn]   val unusedValue = "something"
# [warn]       ^^^^^^^^^^^
# Compiled project (Scala 3.5.1, JVM (17))

Dependencies:

• Misc improvements in compiler options handling #3253