Method GenerateExistsClause(IReadOnlyList<FieldInfo>, string, string)

Generates EXISTS with PVT subquery for WHERE condition (T-SQL syntax).
Uses MAX(CASE WHEN) for scalar fields - single pass optimization.
Supports ListItem.Value/Alias via JOIN with _list_items.
SECURITY: structureIds are parameterized.

public CompiledPvtQuery GenerateExistsClause(IReadOnlyList<FieldInfo> fields, string whereCondition, string tableAlias = "o")