gen_stub: replace FunctionOrMethodName::isMethod() with instanceof

Author: DanielEScherzer

build/gen_stub.php

@@ -955,7 +955,6 @@ public function getArgInfoName(): string;
     public function getMethodSynopsisFilename(): string;
     public function getNameForAttributes(): string;
     public function __toString(): string;
-    public function isMethod(): bool;
     public function isConstructor(): bool;
     public function isDestructor(): bool;
 }
@@ -1015,10 +1014,6 @@ public function __toString(): string {
         return $this->name->toString();
     }
 
-    public function isMethod(): bool {
-        return false;
-    }
-
     public function isConstructor(): bool {
         return false;
     }
@@ -1064,10 +1059,6 @@ public function __toString(): string {
         return "$this->className::$this->methodName";
     }
 
-    public function isMethod(): bool {
-        return true;
-    }
-
     public function isConstructor(): bool {
         return $this->methodName === "__construct";
     }
@@ -1384,7 +1375,7 @@ public function __construct(
 
     public function isMethod(): bool
     {
-        return $this->name->isMethod();
+        return $this->name instanceof MethodName;
     }
 
     public function isFinalMethod(): bool