Parse stdlibPlaceholder in Nockma parser (#3065)

In the nockma parser (e.g used when running `juvix dev nockma run`), the
strings "nil", "functionsPlaceholder", and "stdlibPlaceholder" all parse
to Nockma nil.

We added `stdlibPlaceholder` in:

* #3005

but we forgot to add it to the parser.

src/Juvix/Compiler/Nockma/Translation/FromSource/Base.hs

@@ -135,14 +135,11 @@ atomWithLoc p n = do
   return (set atomLoc (Just loc) n)
 
 atomNil :: Parser (Atom Natural)
-atomNil = symbol Str.nil $> nockNil
+atomNil = choice (map symbol [Str.nil, Str.functionsPlaceholder, Str.stdlibPlaceholder]) $> nockNil
 
 atomVoid :: Parser (Atom Natural)
 atomVoid = symbol Str.void $> nockVoid
 
-atomFunctionsPlaceholder :: Parser (Atom Natural)
-atomFunctionsPlaceholder = symbol Str.functionsPlaceholder $> nockNil
-
 atomStringLiteral :: Parser (Atom Natural)
 atomStringLiteral = do
   WithLoc loc s <- withLoc stringLiteral
@@ -163,7 +160,6 @@ patom = do
     <|> atomBool
     <|> atomNil
     <|> atomVoid
-    <|> atomFunctionsPlaceholder
     <|> try atomStringLiteral
 
 iden :: Parser Text