[SanderMuller]

PHPStan crashes on a partial function application, for example str_replace(' ', '-', ?). The guards in front of getArgs() only skip first-class callables, so a call with a ? placeholder gets through. The crash starts in the parser visitors (assert(!$this->isPartialFunctionApplication()), as in the playground link in the issue) or later in ArgumentsHandler.

This PR does not add precise closure types yet. The result type is Closure, and a follow-up can build the signature from the RFC rules.

• NodeScopeResolver replaces a partial function application with a new virtual node, PartialFunctionApplicationNode, like it does for first-class callables. Its handler processes the callee and the bound arguments, because PHP evaluates them when it creates the closure. Rules for the call itself do not see the original node.
• The guards in front of getArgs() use isPartialFunctionApplication() now. Code that needs a first-class callable, like the pipe operator support, still checks for one.
• A new level 0 rule reports partial function application below PHP 8.6. It also reports $a?->b(?) and new Foo(?), which PHP does not compile. $a?->b(...) crashed before this change too, and now gets the same error.
• ClassStatementsGatherer counts $this->foo(?) as a call, so a private method that only a partial application uses is not reported as unused.
• The Turbo extension has the same changes. The new handler has no C++ mirror, because it only runs for partial applications. I can port it if you want one.

Calls in constant expressions, for example a parameter default strlen(?), get the type Closure too.

Part of phpstan/phpstan#15364

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