Add test for unsetting ReflectionClassConstant::$name

This test was supposed to be part of 50b4a7adf9.

ext/reflection/tests/ReflectionClassConstant_unset_name.phpt

@@ -0,0 +1,28 @@
+--TEST--
+Unsetting name on ReflectionClassConstant
+--FILE--
+<?php
+
+class Test {
+    public const C = 1;
+}
+
+// This is unsupported and the actual behavior doesn't matter.
+// Just make sure it doesn't crash.
+$rc = new ReflectionClassConstant(Test::class, 'C');
+unset($rc->name);
+try {
+    var_dump($rc->getName());
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+try {
+    echo $rc, "\n";
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
+?>
+--EXPECT--
+Typed property ReflectionClassConstant::$name must not be accessed before initialization
+Typed property ReflectionClassConstant::$name must not be accessed before initialization