[12.x] Use Container::getInstance() in ComposerScripts::prePackageUninstall()

[cosmastech]

relying on the result of require_once doesn't work if multiple packages are being uninstalled 😓 require_once returns true the second time it's called (TIL).

Instead, we leverage Container::getInstance() and live happily ever after. 🤞

See discussion: #57220

Thanks to @htulibacki for reporting this and helping test.

[AhmedAlaa4611]

Why do we still need require_once $bootstrapFile; and we have Container::getInstance()?

[cosmastech]

require_once $bootstrapFile fetches the user-defined Application builder. This will resolve the Container's instance during its setup.

The first time you call require_once $bootstrapFile, it does return an instance of Application. If you call it again during the life-cycle, it just returns true. (See the documentation for include_once where this behavior is mentioned).

The reason this is necessary is if you call composer remove laravel/telescope laravel/boost, this does not tear down and reboot the php interpreter for each package being removed. So for the first package removed, ComposerScripts::prePackageUninstall() is called, where require_once DOES return the application, but for the second package require_once just returns true.

Thus, this change:

• ensures we have built the application according to project's application builder (bootstrap/app.php)
• accesses the Application via the Container facade
• ensures if we are removing multiple packages, it still works

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Let me know if that makes sense or if you have any other questions.

[AhmedAlaa4611]

Thanks! That makes sense now. Other small question; do you think we should document the work done in #57144 and laravel/telescope#1641 in the package documentation, so developers can use this feature in their own packages when they need to register a service provider in the bootstrap/providers.php file?