Refactor test traits into just one: HasBrowser

[kbond]

Now any TestCase that uses HasBrowser, has access to all 3 provided browsers (assuming the current test case supports your chosen browser):

class MyTest extends PantherTestCase // this test case supports all 3
{
    use HasBrowser;

    public function test_that_uses_kernel_browser(): void
    {
        $this->kernelBrowser()
            ->visit('/my/page')
            // ...
        ;
    }

    public function test_that_uses_panther_browser(): void
    {
        $this->pantherBrowser()
            ->visit('/my/page')
            // ...
        ;
    }

    public function test_that_uses_http_browser(): void
    {
        $this->httpBrowser()
            ->visit('/my/page')
            // ...
        ;
    }
}

This also removes ambiguous methods (ie ->createBrowser()) from the HasBrowser trait that could be confusing.

TODO

• Update tests
• Update docs