Support DML with statements hints

[apstndb]

DMLs with statement hints are not yet supported.

https://cloud.google.com/spanner/docs/reference/standard-sql/dml-syntax#delete-statement

[statement_hint_expr] DELETE [FROM] table_name [table_hint_expr] [[AS] alias] WHERE condition [return_clause];

https://cloud.google.com/spanner/docs/reference/standard-sql/dml-syntax#update-statement

[statement_hint_expr] UPDATE table_name [table_hint_expr] [[AS] alias]

$ go run ./tools/parse --mode dml '@{PDML_MAX_PARALLELISM=1} UPDATE DMLTest SET Col = 1 WHERE TRUE'      
2024/10/01 23:54:37 syntax error::1:1: expected token: <ident>, but: @

  1:  @{PDML_MAX_PARALLELISM=1} UPDATE DMLTest SET Col = 1 WHERE TRUE
      ^
exit status 1

$ go run ./tools/parse --mode dml '@{PDML_MAX_PARALLELISM=1} UPDATE DMLTest SET Col = 1 WHERE TRUE'      
2024/10/01 23:54:14 syntax error::1:1: expected token: <ident>, but: @

  1:  @{PDML_MAX_PARALLELISM=1} UPDATE DMLTest SET Col = 1 WHERE TRUE
      ^
exit status 1