[3.x] Fix conflicts with PHP's predefined classes

[PerryvanderMeer]

This PR fixes the problem described in discussion #8248.

Problem

When you have a component in Livewire's root class namespace that matches any of PHP's predefined classes, subsequent requests won't work.

So, an initial request for the component App\Livewire\Directory works, but subsequent requests won't. Those will trigger Livewire's ComponentNotFoundException:

Unable to find component: [directory]

Note: when the component is located as App\Livewire\Foo\Directory, also subsequent requests will work.

Cause

For subsequent requests, Livewire will try to resolve the requested component's location.
Initially, it will check if a class exists for the requested component:

livewire/src/Mechanisms/ComponentRegistry.php

Line 90 in 4f86fc1

if (class_exists($nameOrClass)) {

For App\Livewire\Directory (which will be requested as directory), this will return true, because class_exists('directory') returns true as it matches PHP's predefined class. Note: that is also the explanation why locating App\Livewire\Foo\Directory works, because class_exists('foo.directory') won't conflict.

Solution

We can extend the class existance-check with a check if the found class also extends Livewire's Component class. Obviously PHP's predefined class does not comply with that, while App\Livewire\Directory will.

[calebporzio]

Ahhhhh that's a tricky one, I think I was actually bit by this recently. Thanks! (and thanks for the super clear PR writeup!)