[ docs ] Add record field docstrings to the RF-name as well

A record field can add two names to the context, a UN-name and an
RF-name.  The docstring is now saved for both names, so that it can
always be found when one of the names can be resolved.

Previously the docstring was only saved for the UN-name which led to the
docs missing when looking up the (.fieldName) version, e.g. when listing
docs for the record type.

src/Idris/Desugar.idr

@@ -770,10 +770,15 @@ mutual
                  Core IField
   desugarField ps ns (MkField fc doc rig p n ty)
       = do addDocStringNS ns n doc
+           addDocStringNS ns (toRF n) doc
            syn <- get Syn
            pure (MkIField fc rig !(traverse (desugar AnyExpr ps) p )
                           n !(bindTypeNames fc (usingImpl syn)
                           ps !(desugar AnyExpr ps ty)))
+        where
+          toRF : Name -> Name
+          toRF (UN n) = RF n
+          toRF n = n
 
   export
   desugarFnOpt : {auto s : Ref Syn SyntaxInfo} ->