Support PLACEMENT KEY in column definition

[apstndb]

Syntax

https://cloud.google.com/spanner/docs/reference/standard-sql/data-definition-language#create_table

CREATE TABLE [ IF NOT EXISTS ] table_name ( [
   { column_name data_type [NOT NULL]
     [ { DEFAULT ( expression ) | AS ( expression ) [ STORED ]
       | GENERATED BY DEFAULT AS IDENTITY [ ( sequence_option_clause ... ) ] } ]
     [ PRIMARY KEY ]
     [ options_def ]
   | location_name STRING(MAX) NOT NULL PLACEMENT KEY
   | table_constraint
   | synonym_definition }
   [, ... ]
] )

Example

https://cloud.google.com/spanner/docs/create-manage-data-placements#create-table

CREATE TABLE Singers (
  SingerId INT64 NOT NULL,
  SingerName STRING(MAX) NOT NULL,
  Location STRING(MAX) NOT NULL PLACEMENT KEY
) PRIMARY KEY (SingerId);

• related with Support CREATE PLACEMENT statement #165

[apstndb]

May it be better to be parsed as {PRIMARY|PLACEMENT} KEY, but it requires a breaking change.
(I believe that there is no user pasing inline PRIMARY KEY.)