Chromeless app container should occupy entire screen

[azasypkin]

Chromeless app container should occupy entire screen, like legacy hidden apps did. Currently there is still top and left "margin" for invisible Chrome header and nav bar (see screenshot below).

Steps to reproduce:

1. Define the app:

core.application.register({
  appRoute: '/some',
  chromeless: true,
  id: 'some',
  title: 'some',
  mount({ element }) {
    function SomeComponent() {
      return <div>Some</div>;
    }
    render(<SomeComponent />, element);
    return () => {
      unmountComponentAtNode(element);
    };
  },
});

2. Define the custom app route:

router.get(
  { path: '/some', validate: false },
  async (context, request, response) => {
    return response.ok({
        body: await context.core.rendering.render({ includeUserSettings: false }),
        headers: { 'content-security-policy': csp.header },
      });
  })
);

3. Try to open http://localhost:5601/some in the browser.

Screenshots (if relevant):

/cc @eliperelman @legrego

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)

[pgayvallet]

Caused by

kibana/src/core/public/rendering/rendering_service.tsx

Lines 68 to 73 in 812c950

	<div className="app-wrapper">
	<div className="app-wrapper-panel">
	<div id="globalBannerList">{bannerUi}</div>
	<div className="application">{appUi}</div>
	</div>
	</div>

The app-wrapper does not have the hidden-chrome class when a chromeless app is mounted in non-legacy mode.