Initial view should properly reflect fields that are on or off

Setting ['#attributes']['checked'] isn't a totally valid way to do this. I know that ['#default_value'] doesn't work as expected for an exposed form, but here's a case where ['#attributes']['checked'] doesn't work:
Create a view on Article with the following fields:
Content: Title
Content: Authored by (Authored by)
Content: Authored on (Authored on) [hidden]
Content: Body (Body)
Content: Content type (Content type)
Content: ID (ID) [hidden]
Content: Tags (Tags)
Global: On/Off Form (On/Off Form)

The On/Off Form only allows selection of visible fields (and I'm not sure when it started doing that - I thought that previously, it allowed selection of fields whether they were visible or not, which I think it should do), so leave them all visible. Select all of the fields in the On/Off form, then edit "Authored on" to Excluded.

Now, when you go to the view, all of the fields are checked, even though "Authored on" isn't visible. We need to be able to set the checked fields individually. I started working on this and found that ['#default_value'] didn't work as expected in the exposed form.

For instance, if you create a standard form and display it, this behaves correctly:

$options = [
      'one' => 'One',
      'two' => 'Two',
      'three' => 'Three',
    ];
    $defaultValues = ['two'];
    $form['checkboxes'] = [
      '#type' => 'checkboxes',
      '#title' => $this->t('Test'),
      '#description' => t('Select the fields you want to display.'),
      '#options' => $options,
      '#default_value' => $defaultValues,
    ];

If you paste that into the exposed form, the default value for a checkboxes element is ignored (note that #default_value works for other controls on an exposed form, and that it works for checkboxes on another form, but for checkboxes on an exposed form, it doesn't work). If we can't use the default value or attributes for the whole checkboxes element, we need some other way to check them individually. I don't have that other way yet :)

So we don't lose this experiment for testing:

    $options = [
      'one' => 'One',
      'two' => 'Two',
      'three' => 'Three',
    ];
    $defaultValues = ['two'];
    $form['checkboxes'] = [
      '#type' => 'checkboxes',
      '#title' => $this->t('Test'),
      '#description' => t('Select the fields you want to display.'),
      '#options' => $options,
      '#default_value' => $defaultValues,
    ];

    $form['select'] = [
      '#type' => 'select',
      '#options' => $options,
      '#title' => $this->t('Order3', [], ['context' => 'Sort order']),
      '#default_value' => ['three'],
    ];

If we add the code above to a regular form, then the "Two" checkbox will be selected by default, and the "Three" option will be selected by default.
If we add this code to the exposed form, then the checkboxes are all un-checked and the "Three" option will be selected by default.