Add tests proving isset() still reports for properties with default values

Properties with default values (e.g. `private int $bar = 1;`) are handled
by `hasDefaultValue()` in IssetCheck, not by PropertyInitializationExpr.
Removing PropertyInitializationExpr entries for methods called from the
constructor does not affect properties with defaults — they are still
correctly flagged.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

tests/PHPStan/Rules/Variables/IssetRuleTest.php

@@ -567,14 +567,24 @@ public function testBug13473(): void
 	{
 		$this->treatPhpDocTypesAsCertain = true;
 
-		$this->analyse([__DIR__ . '/data/bug-13473.php'], []);
+		$this->analyse([__DIR__ . '/data/bug-13473.php'], [
+			[
+				'Property Bug13473\FooWithDefault::$bar (int) in isset() is not nullable.',
+				28,
+			],
+		]);
 	}
 
 	public function testBug13473Method(): void
 	{
 		$this->treatPhpDocTypesAsCertain = true;
 
-		$this->analyse([__DIR__ . '/data/bug-13473-method.php'], []);
+		$this->analyse([__DIR__ . '/data/bug-13473-method.php'], [
+			[
+				'Property Bug13473Method\FooWithDefault::$bar (int) in isset() is not nullable.',
+				34,
+			],
+		]);
 	}
 
 }

tests/PHPStan/Rules/Variables/data/bug-13473-method.php

@@ -20,3 +20,20 @@ public function setBar(int $bar): void
 		$this->bar = $bar;
 	}
 }
+
+class FooWithDefault {
+    private int $bar = 1;
+
+    public function __construct(int $bar)
+    {
+        $this->setBar($bar);
+    }
+
+	public function setBar(int $bar): void
+	{
+		if (isset($this->bar)) {
+			throw new \Exception('bar is set');
+		}
+		$this->bar = $bar;
+	}
+}

tests/PHPStan/Rules/Variables/data/bug-13473.php

@@ -20,3 +20,20 @@ public function __construct(int $bar)
 		$this->bar = $bar;
 	}
 }
+
+class FooWithDefault {
+	private(set) int $bar = 1 {
+		get => $this->bar;
+		set(int $bar) {
+			if (isset($this->bar)) {
+				throw new \Exception('bar is set');
+			}
+			$this->bar = $bar;
+		}
+	}
+
+	public function __construct(int $bar)
+	{
+		$this->bar = $bar;
+	}
+}