JuliaSyntax: Remove `@ref`s to `RawGreenNode` (#63207)
JuliaSyntax: Stop cross-referencing `RawGreenNode` from public docstrings
`RawGreenNode` is internal, so it has no entry in the API reference for these
links to resolve to. Mention it as plain code instead.
Assisted-by: Claude Code (Opus 5)
