Add possibility of adding an INDEX (or KEY) as a "constraint" to DDL statements

[lukaseder]

MySQL allows for treating indexes as constraints, syntactically, in DDL statements. From the manual:

create_definition:
    col_name column_definition
  | [CONSTRAINT [symbol]] PRIMARY KEY [index_type] (index_col_name,...)
      [index_option] ...
  | {INDEX|KEY} [index_name] [index_type] (index_col_name,...) -- This clause here
      [index_option] ...
  | [CONSTRAINT [symbol]] UNIQUE [INDEX|KEY]
      [index_name] [index_type] (index_col_name,...)
      [index_option] ...
  | {FULLTEXT|SPATIAL} [INDEX|KEY] [index_name] (index_col_name,...)
      [index_option] ...
  | [CONSTRAINT [symbol]] FOREIGN KEY
      [index_name] (index_col_name,...) reference_definition
  | CHECK (expr)

It would be great to support this in the jOOQ API and in the parser (see #7347) and emulate it in other databases using an anonymous block.

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See:

• https://dev.mysql.com/doc/refman/8.0/en/create-table.html