Add a Multiline option for CASE expressions (WHEN/THEN/ELSE on their own lines)

Bắt đầu bằng cách đọc SqlScriptGeneratorOptions và hành vi của Sql170ScriptGenerator đối với các tùy chọn Multiline* hiện có, sau đó so sánh cách các biểu thức CASE được phát sinh. Truy vết các bài kiểm thử generator liên quan nếu có, và xác minh rằng mặc định vẫn giữ đầu ra inline, trong khi MultilineCaseExpression đặt các nhánh WHEN và ELSE trên những dòng riêng được thụt lề.

Is your feature request related to a problem? Please describe

When Sql170ScriptGenerator regenerates a script, a CASE expression is always emitted inline — every
WHEN/THEN/ELSE is joined onto one logical line. For multi-branch CASE expressions this makes the
output substantially harder to read than the input, and where a WHEN predicate has multiple conjuncts
the hanging indent compounds: each AND is indented to the width of the preceding WHEN, and the next
WHEN is then appended after that indented continuation, producing a staircase.

Input (longest line 81 chars):

SELECT CASE
           WHEN o.status = 'P' AND o.paid_amount >= o.total_amount THEN 'settled'
           WHEN o.status = 'P' AND o.paid_amount > 0 THEN 'part-paid'
           WHEN o.status = 'C' THEN 'cancelled'
           ELSE 'open'
       END AS settlement_state,
       CASE WHEN o.due_date < SYSUTCDATETIME() THEN 1 ELSE 0 END AS is_overdue
FROM orders AS o
WHERE o.tenant_id = 42;

Output with MultilineSelectElementsList = true, IndentationSize = 4 (longest line 185 chars):

SELECT CASE WHEN o.status = 'P'
                 AND o.paid_amount >= o.total_amount THEN 'settled' WHEN o.status = 'P'
                                                                         AND o.paid_amount > 0 THEN 'part-paid' WHEN o.status = 'C' THEN 'cancelled' ELSE 'open' END AS settlement_state,
       CASE WHEN o.due_date < SYSUTCDATETIME() THEN 1 ELSE 0 END AS is_overdue
FROM   orders AS o
WHERE  o.tenant_id = 42;

An 81-character input becomes a 185-character line. There is currently no option that affects this:
of the 46 properties on SqlScriptGeneratorOptions, none matches Case or When, and none provides a
maximum line width. AlignClauseBodies, ClauseBodyAlignment and the Multiline* options do not reach
inside a CASE.

Describe the solution you'd like

A MultilineCaseExpression option (default false, preserving current output) that places each WHEN
branch and the ELSE on its own line, indented one level from the CASE:

SELECT CASE
           WHEN o.status = 'P' AND o.paid_amount >= o.total_amount THEN 'settled'
           WHEN o.status = 'P' AND o.paid_amount > 0 THEN 'part-paid'
           WHEN o.status = 'C' THEN 'cancelled'
           ELSE 'open'
       END AS settlement_state,

This fits the existing naming and behaviour of the Multiline* family —
MultilineSelectElementsList, MultilineWherePredicatesList, MultilineInValuesList,
MultilineViewColumnsList, MultilineSetClauseItems, MultilineInsertTargetsList,
MultilineInsertSourcesList, MultilineProcedureParametersList — so it should need no new concepts.

A single-branch CASE staying inline when the option is off (as
CASE WHEN … THEN 1 ELSE 0 END above) seems the right default; whether a one-branch CASE should also
break under the option is a judgement call I have no strong view on.

Describe alternatives you've considered

• Existing options — AlignClauseBodies, ClauseBodyAlignment = Indented,
  MultilineSelectElementsList, and reduced IndentationSize. None affects the interior of a CASE;
  the best combination I found did not shorten these lines.
• A general maximum-line-width option. More broadly useful, but a much larger change and a different
  model from the current per-construct toggles, so I have not requested it here.
• Post-processing the generated text. Re-wrapping CASE with a regex outside the generator defeats
  the point of using an AST-based formatter and is not reliable in the presence of string literals.

Additional context

• Microsoft.SqlServer.TransactSql.ScriptDom 180.78.1 (assembly 18.0.0.0), net8.0; behaviour is the
  same on Sql160ScriptGenerator, Sql170ScriptGenerator and Sql180ScriptGenerator.
• Related open requests of the same shape, both asking for a construct to be broken across lines:
  #189 (INSERT columns) and #21 (stored-procedure parameters).
• Happy to test a change against a large real-world T-SQL corpus if that is useful.