[skip ci]

This'll fix #23437 (eventually, patience plz)

The PR should not be merged as such, since there are a few additions
and changes to the build files as well as development files & folders that do not belong into the main branch.

TODOs

• Rendering of capture sets
• Rendering of various arrows
  • Clarify: Include context function arrows?
  • Clarify: Are arrows without any capture annots by default pure?
  • Fix rendering logic for dependent function arrows
  • Test polymorphic functions
• Rendering of paths in capture sets
• Rendering of reach capabilities
• Rendering of capture variables
  • Rendering of capture members
  • Rendering of the hat symbol on polymorphic funs
  • Rendering of the hat in HK types
• Rendering of update
• Rendering of @consume, @use
• Rendering of .rd
• Test type refinements
• Fix some minor rendering bugs with paths and parameters
• Rendering inherited members of pure subclasses
  • Does it make sense to have a badge/indicator that the current file is capture checked?
• Option to suppress CC completely
• Support rendering of classifier capabilities once merged.
• Fix the mess with context parameters for tree traversals. (Follow-up PR)
• Host the stdlib cc scaladoc somewhere
  • Link to it in the vanilla api docs (and back from cc version)

I think for now, let's have a separate API doc for CC enabled. A follow-up PR can investigate how to have one doc and a toggle on the page. This also depends to some extent on the effort to have a Scala 3 library artifact #22043 as well as having the rest of the standard library capture checked.

Trying it Out

1. Scala 2 library CC (slow): Just run scaladoc/generateScalaDocumentation in sbt, go to ./scaladoc/output, and run an HTTP server from there to browse the API for the capture-checked stdlib.
2. Small example project (faster) located in ./local/project. In sbt, invoke myrefresh which will compile the example project and then run scaladoc on it. The scaladoc output is in ./local/api and can be viewed using a local HTTP server.
   • If you change the example project, always run myrefresh afterwards for the up-to-date scaladoc.
   • If you changed the scaladoc source, but did not touch the example project, it suffices to run myscaladoc in sbt.