Refactor filesystem mocks

[ghostwriter]

• Mock Filesystem inside TestCase.php
• Removed MocksFilesystem trait

[jasonmccreary]

I vaguely remember there being an issue when using Illuminate\Filesystem\Filesystem directly. That's why these used the contract.

It won't be something that appears in the tests since we're mocking, but it will be an issue at runtime. Especially if someone has swapped it out in the container. However, I'm not sure if we'd want to use that anyway. So it's probably fine, but wanted to brain dump before merging to get your thoughts...

[ghostwriter]

• tests were only partially mocking the class.
• inconsistent usage (concrete/interface)

Blueprint uses both \Illuminate\Contracts\Filesystem\Filesystem and Illuminate\Filesystem\Filesystem interchangeably.

Which I understand as, it accepts the concrete class in some places instead of the interface, and the tests partially mocks the interface.

To your point, i’ll update this PR to use the concrete implementation (I assume since Blueprint is specifically for Laravel, devs wouldn’t need a 3rd party library for filesystem when one is provided “out of the box”.)

[jasonmccreary]

@nathane, I'm fine either way. To your point, just want it to be consistent.

[jasonmccreary]

Whatever recent commit you made had very opinionated formatting and importing rules.

[jasonmccreary]

@nathane, best to undo the "scouting" commit. It has all sort of opinionated formatting and the class reference, while I generally agree with, actually make the code harder to test since it's not within the Laravel framework.