Add support for calling commands from an actual Scala language installation in `sclicheck`

[Gedochao]

Describe what needs to be done and why As per https://github.com/VirtusLab/scala-cli/pull/3155:

• the scala command in docs-tests is currently just an alias for scala-cli, rather than a 1:1 use of the scala wrapper from scala:3.5.0 installation
• scalac and scala_legacy are currently launched through their main classes with scala-cli, rather than via an actual installation (although that's largely the same, just slower)
• we should swap scala, scalac and scala_legacy to an actual coursier installation of the default Scala version when using sclicheck.

Is your feature request related to a past ticket or discussion?

• https://github.com/VirtusLab/scala-cli/pull/3155

Describe alternatives you've considered The current workaround mimics an actual Scala 3 installation close enough for our docs to be largely testable, so we might also just leave it as it is, if we won't have the time to implement this.