Implements #21928
Adds a `--raw` (since thats what the original issue used, suggestions
welcome) switch which stops the jsondoc gen from rendering rst/markdown.
Implemented by making `genComment` check if it needs to return the raw
string or not. This required switching the related procs to using
`Option` to handle how `nil` values were returned before. The `nil`
returns were eventually ignored so just ignoring `none(T)` has the same
effect.
Doesn't support `runnableExamples` since jsondocs doesn't support them
either
(cherry picked from commit c1e381ae8d)
