[5.8] allow view assertions to see all data

[browner12]

Problem

The assertViewHas() assertion in the HTTP testing will currently only look at data bound directly to the view, and not data that has been 'shared' with the view. This makes it a little clunkier to check for shared data.

$response = $this->get('/');

$response->assertOk();

$response->assertViewHas('someKey');  // fails with shared data

$this->assertArrayHasKey('someKey', $response->original->gatherData());

Solution

The view assertions now use the gatherData() method, instead of the getData() method, which provides us both the directly bound data, and the globally shared data.

Concerns

• Is this BC kosher? Not sure if this would be considered a 'bug fix' or a 'change of behavior', and I guess depends on the intent of the assertion.
• Or does this belong in a separate assertion? assertViewHasShared() or something similar?