docs migration - Swift Compiler

Start by reviewing documentation/swift-compiler/index.md and the included _compiler-architecture.md content. First coordinate with the compiler team to determine the destination and disposition; completion requires carrying out the selected migration, validation, preview, review, and redirect steps listed in the checklist.

Source: documentation/swift-compiler/index.md
Proposed disposition: Needs determination — this page covers the compiler's source repository layout and high-level architecture (via _compiler-architecture.md include). The proposal notes the Swift compiler has a userdocs directory that is the right long-term home for compiler documentation. Consider whether this page redirects there, migrates to a catalog in this repository, or retains its current form on swift.org.
Reviewer: @swiftlang/language-steering-group

Note: The _compiler-architecture.md include file is incorporated into this page.

Checklist

• Create a GitHub issue to track this migration once destination is confirmed (if migrating)
• Determine disposition and choose explicit destination (coordinate with compiler team regarding the userdocs direction)
• Review source for accuracy against current compiler architecture
• Decide how to handle _compiler-architecture.md include content
• If migrating: translate Jekyll markdown to DocC markdown format
  • Remove YAML front matter
  • Inline content from _compiler-architecture.md or create a separate article
  • Convert any Jekyll callouts to DocC-style callouts
• If migrating: add article(s) to target catalog's Documentation.md
• Run swift package generate-documentation --analyze --warnings-as-errors in the target package
• Preview locally with swift package --disable-sandbox preview-documentation
• Submit PR for appropriate team review
• After merge and publication: add redirect_to: in the swift.org source file's front matter
• Submit redirect PR to swift-org-website