Add a test involving a trait

Author: nikic

Zend/tests/type_declarations/static_type_trait.phpt

@@ -0,0 +1,38 @@
+--TEST--
+static type in trait
+--FILE--
+<?php
+
+trait T {
+    public function test($arg): static {
+        return $arg;
+    }
+}
+
+class C {
+    use T;
+}
+class P extends C {
+}
+
+$c = new C;
+$p = new P;
+var_dump($c->test($c));
+var_dump($c->test($p));
+var_dump($p->test($p));
+var_dump($p->test($c));
+
+?>
+--EXPECTF--
+object(C)#1 (0) {
+}
+object(P)#2 (0) {
+}
+object(P)#2 (0) {
+}
+
+Fatal error: Uncaught TypeError: Return value of C::test() must be an instance of P, instance of C returned in %s:%d
+Stack trace:
+#0 %s(%d): C->test(Object(C))
+#1 {main}
+  thrown in %s on line %d