Before this commit, the error was reported with ERRCODE_INTERNAL_ERROR
(SQLSTATE XX000):

```
postgres=# \set VERBOSITY verbose
postgres=# select 'foo'::ulid;
ERROR:  XX000: invalid input syntax for type ulid: "foo": invalid length
LINE 1: select 'foo'::ulid;
               ^
LOCATION:  lib.rs:37
```

With this, ERRCODE_INVALID_TEXT_REPRESENTATION (SQLSTATE 22P02) is used:

```
postgres=# \set VERBOSITY verbose
postgres=# select 'foo'::ulid;
ERROR:  22P02: invalid input syntax for type ulid: "foo": invalid length
LINE 1: select 'foo'::ulid;
               ^
LOCATION:  <ulid::ulid as pgrx::inoutfuncs::InOutFuncs>::input, lib.rs:39
```