MsSql: Keep the comma separator when displaying DECLARE lists

[LucaCappelletti94]

In MsSql one DECLARE keyword takes a comma-separated list of declarations, DECLARE @a INT, @b INT (https://learn.microsoft.com/en-us/sql/t-sql/language-elements/declare-local-variable-transact-sql). The parser collected the list into one Statement::Declare, but the display joined it with ; , so the statement was printed back as DECLARE @a INT; @b INT, which T-SQL reads as a different statement.

Statement::Declare gains a separator: DeclareSeparator field. The MsSql parser records Comma, and the Snowflake, BigQuery and cursor forms record Semicolon, matching Snowflake Scripting's DECLARE section where each declaration ends with ; (https://docs.snowflake.com/en/sql-reference/snowflake-scripting/declare).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.26%. Comparing base (1aabd12) to head (b634c00).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2671      +/-   ##
==========================================
+ Coverage   81.25%   81.26%   +0.01%     
==========================================
  Files          42       42              
  Lines       33910    33920      +10     
  Branches    33910    33920      +10     
==========================================
+ Hits        27553    27566      +13     
+ Misses       2792     2790       -2     
+ Partials     3565     3564       -1     

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