feat: unused views collector rule

[canvural]

• Added or updated tests
• Documented user facing changes
• Updated CHANGELOG.md

This PR adds a new rule that can find the unused views, using PHPStan's collector feature. It'll be an optional rule.

Some concerns

• Collectors for this feature tries to find used views in 2 places currently: view('foo') calls. And $this->markdown('foo') in any Mailable class. Are there more places that we can check?
• Currently there are false positives if a view is only used in another view. For example with @extends('foo') I'd say this is an edge case, and can be ignored by the user.

Todos

• This error should not happen. The mentioned views are from the dummy Laravel project Testbench created, not from the actual package.
• Support View::make('foo') and $viewFactory->make()
• Support $this->view('foo') in Mailables

How to test it?

Run composer require --dev nunomaduro/larastan:dev-unused-views Then run your PHPStan analysis again.
And report here if there are any false positives or errors that we can fix!

[mad-briller]

Are there more places that we can check?

Alongside the view facade, the View\Factory contract may be injected and $viewFactory->make() called instead, so may be worth checking there too

[canvural]

Thanks, updated the list.