Cannot parse named windows with modifiers

[jesse-shopify]

sqlparser-rs only supports named windows that are an identifier. This is fine for queries like:

SELECT sum(salary) OVER w, avg(salary) OVER w
  FROM empsalary
  WINDOW w AS (PARTITION BY depname ORDER BY salary DESC);

However, it is insufficient for queries in at least BigQuery and MySQL where modifiers can be added to the named window in the OVER clause.

MySQL named window example

SELECT
  DISTINCT year, country,
  FIRST_VALUE(year) OVER (w ORDER BY year ASC) AS first,
  FIRST_VALUE(year) OVER (w ORDER BY year DESC) AS last
FROM sales
WINDOW w AS (PARTITION BY country)

BigQuery named window example

SELECT item, purchases, category, LAST_VALUE(item)
  OVER (
    item_window
    ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING
  ) AS most_popular
FROM Produce
WINDOW item_window AS (
  PARTITION BY category
  ORDER BY purchases)

This would build upon prior to work:

• Add support for named window frames #867
• Named window frames #881

[alamb]

Thanks for the report @jesse-shopify -- any contributions to add such support are most welcome