feat: Add WITH OFFSET Alias

[sivchari]

I add With Offset alias.

[coveralls]

Pull Request Test Coverage Report for Build 2563712058

• 23 of 25 (92.0%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.005%) to 89.787%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/parser.rs	4	6	66.67%

Files with Coverage Reduction	New Missed Lines	%
src/ast/query.rs	1	86.61%

Totals
Change from base Build 2535757386:	0.005%
Covered Lines:	8791
Relevant Lines:	9791

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💛 - Coveralls

[alamb]

Thank you @sivchari -- can you point me at what systems use this syntax ? I tried to find it in the mysql manual but I couldn't quite figure it out

[sivchari]

from_item:
    {
      table_name [ as_alias ] [ FOR SYSTEM_TIME AS OF timestamp_expression ]
      | { join_operation | ( join_operation ) }
      | ( query_expr ) [ as_alias ]
      | field_path
      | unnest_operator
      | cte_name [ as_alias ]
    }

unnest_operator:
    {
      [UNNEST](https://cloud.google.com/bigquery/docs/reference/standard-sql/query-syntax#unnest)( array_expression )
      | UNNEST( array_path )
      | array_path
    }
    [ as_alias ]
    [ WITH OFFSET [ as_alias ] ]

https://cloud.google.com/bigquery/docs/reference/standard-sql/query-syntax#unnest_operator

I forgot to support WITH OFFSET Alias in #493 , so I added it.

[alamb]

Thanks @sivchari and @Dandandan