Refactor how redirections are represented by the tokenizer

Prior to this fix, each redirection type was a separate token_type.
Unify these under a single type TOK_REDIRECT and break the redirection
type out into a new sub-type redirection_type_t.

src/parse_tree.cpp

@@ -231,11 +231,7 @@ static inline parse_token_type_t parse_token_type_from_tokenizer_token(
             result = parse_token_type_background;
             break;
         }
-        case TOK_REDIRECT_OUT:
-        case TOK_REDIRECT_APPEND:
-        case TOK_REDIRECT_IN:
-        case TOK_REDIRECT_FD:
-        case TOK_REDIRECT_NOCLOB: {
+        case TOK_REDIRECT: {
             result = parse_token_type_redirection;
             break;
         }