Support for printing help from scala compiler

[lwronski]

Is your feature request related to a problem? Please describe.

Scala CLI should print help message from scala compiler like scalac -help. It can be added new flag to print help from compiler.

[SethTisue]

scalac -Xshow-phases is also like this:

% /usr/local/scala/scala-2.13.8/bin/scala -Xshow-phases
    phase name  id  description
    ----------  --  -----------
        parser   1  parse source into ASTs, perform simple desugaring
         namer   2  resolve names, attach symbols to named trees
...

but:

% scala-cli compile -S 2.13.8 -Xshow-phases
No inputs provided (expected files with .scala or .sc extensions, and / or directories).

[SethTisue]

similarly, scalac -X and scalac -Y and scalac -V and scalac -W print help for just those subcategories of flags