._name after ) or ] fails with "Unexpected character '_'" #2803

Field access with a name starting with _ fails to tokenize when it follows ) or ]:

SELECT (c)._x FROM tt            (PostgreSqlDialect)
  -> sql parser error: Unexpected character '_' at Line: 1, Column: 11
SELECT ({'_x': 1})._x            (DuckDbDialect)
  -> Unexpected character '_' at Line: 1, Column: 19
SELECT ([{'_a': 2}])[1]._a       (DuckDbDialect)
  -> Unexpected character '_' at Line: 1, Column: 24
SELECT f()._x                    (BigQueryDialect)
  -> Unexpected character '_' at Line: 1, Column: 11
SELECT (c).x FROM tt, SELECT t._x FROM t
  -> parse (fine)

PostgreSQL 18 runs SELECT (c)._x FROM tt for a composite column with a field _x (https://www.postgresql.org/docs/current/rowtypes.html#ROWTYPES-ACCESSING), and DuckDB runs SELECT ({'_x': 1})._x, ([{'_a': 2}])[1]._a (returns 1 | 2).

In Tokenizer::next_token, the ._ check only accepts a preceding Token::Word; after RParen or RBracket it errors. The block right after it already treats . after Word | RParen | RBracket | Number as a period when supports_tuple_element_access(). Related: #1835 (added the check), #2677 (whitespace case).

Tested on main ce12f1f (also 0.63.0 and 0.58.0).

Found with a property-based fuzzer (round trip check); I used AI assistance for triage and verified every case above.