Add fix command for extracting using directives into project.scala file

[MaciejG604]

Fixes #2104

Introduces a new subcommand fix that extracts all using directives that exist througout the project sources (not only files on disk but everything that's linked to the project build). Those extracted directives are then written to project.scala file.

This process can be split into two parts (their order is not exactly 1. -> 2. in code):

1. Extraction of directives and writing them into project.scala
2. Modification of directives in their original sources.

Rules regarding the 1. part:

• if a source contains any target using directive then it's directives are not extracted, since it's a correct way to create projects with cross-configuration (the warning about using directives in multiple files has been modified accordingly)
• directives from sources belonging to the Test scope are extracted and written to project.scala using their test. equivalents (using dep -> using test.dep) if possible, if not possible they are not written to project.scala

Rules regarding the 2. part:

• if a source is writable (is on local disk) and it is a member of original inputs then the extracted directives are removed from its contents, otherwise no modification takes place
• if a source belonging to the Test scope contains directives that do not have test. equivalents they are kept in this source and are not moved to project.scala, all the others extracted using directives are removed from the source if rule above applies

[mpkocher]

Where are the requirements of this defined? I'm not really seeing anything in the original issue.

You're adding a new subcommand called "fix"?

[MaciejG604]

Where are the requirements of this defined? I'm not really seeing anything in the original issue.

The requirements for this were discussed internally by the Scala CLI team. I can list them in the description since they are quite simple.

You're adding a new subcommand called "fix"?

Yes, the proposal right now is to add this functionaility in a fix subcommand. However, all suggestions are highly appreciated.