Fix unidoc

[jackkoenig]

Unidoc was apparently not running in CI and it was broken by #2277. The issue isn't that #2277 is broken, it's that it exposed the fact that unidoc actually runs the same scalacOptions on all of the files being built into 1 doc. This is a problem because Chisel3 core needs to not have the compiler plugin run on it, while the downstream chisel project does. This is a hacky solution, but it's the best I have, see sbt/sbt-unidoc#107.

Note that this has 3 useful commits. There is a little of refactoring of how the plugin skips components (a component is a Scalac compiler phase).

Contributor Checklist

• [NA] Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• [NA] Did you add appropriate documentation in docs/src?
• Did you state the API impact?
• Did you specify the code generation impact?
• Did you request a desired merge strategy?
• [NA] Did you add text to be included in the Release Notes for this change?

Type of Improvement

• bug fix
• documentation

API Impact

This adds an argument to the chisel3 plugin -P:chiselplugin:INTERNALskipFile:<filename>, note this is only intended to be used for internal unidoc generation.

Backend Code Generation Impact

No impact

Desired Merge Strategy

• Rebase

Release Notes

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels?
• Did you mark the proper milestone (Bug fix: 3.3.x, [small] API extension: 3.4.x, API modification or big change: 3.5.0)?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you mark as Please Merge?