[Symfony30] Reuse existing untyped $request param in GetRequestRector

[TomasVotruba]

GetRequestRector added a new Request $request param whenever a @Route action used $this->getRequest(). If the action already had an untyped $request param, the rule renamed the new one to $mainRequest (via resolveUniqueName), producing two request params - one of them dead:

public function someAction($request, Request $mainRequest)

Now the rule reuses an existing untyped $request param and just adds the type:

public function someAction(Request $request)

An already-typed $request (different type) keeps the previous rename behavior, so existing fixtures stay green. New fixture covers the untyped case.