Incorrect type in SelectStatement::$expr when query has CASE-clause in selected fields

从 issue 中的 Parser 复现开始，检查选择 CASE 子句时 SelectStatement::$expr 是如何填充的。比较 Expression 和 CaseExpression 类型，并通过重新运行所提供的脚本来验证预期的契约；完成的标准是报告的 TypeError 不再发生，同时表达式列表仍保持正确的类型。

The public field SelectStatement::$expr is defined in a PHP docblock as an Expression[]. When parsing a query with a CASE statement, a CaseExpression object is present in this list, despite CaseExpression not extending Expression. This causes issues when explicitly requiring the Expression type as should be returned by SelectStatement::$expr.

Reproduction case

<?php

declare(strict_types=1);

use PhpMyAdmin\SqlParser\Components\Expression;
use PhpMyAdmin\SqlParser\Parser;
use PhpMyAdmin\SqlParser\Statements\SelectStatement;

include_once 'vendor/autoload.php';

$p = new Parser('SELECT a, CASE WHEN b IS NOT NULL THEN 1 ELSE 0 END as c FROM t');

$stmt = $p->statements[0];
if (! $stmt instanceof SelectStatement) {
    throw new Exception('Could not parse select statement');
}

function acceptExpression(Expression $e): void {}

$expressions = $stmt->expr;
foreach ($expressions as $expression) {
    acceptExpression($expression);
}

Expected behavior

I would expect this script to not error out as the $stmt->expr returns Expression[] according to its PHP docblock. Each element should therefore be compatible with Expression in my acceptExpression function.

Real behavior

$ php test.php
PHP Fatal error:  Uncaught TypeError: acceptExpression(): Argument #1 ($e) must be of type PhpMyAdmin\SqlParser\Components\Expression, PhpMyAdmin\SqlParser\Components\CaseExpression given, called in /path/to/test.php on line 22 and defined in /path/to/test.php:18
Stack trace:
#0 /path/to/test.php(22): acceptExpression()
#1 {main}
  thrown in /path/to/test.php on line 18