Fix createTestMediaPlayer

[TakayoshiKochi]

Some shadow DOM tests use common "testcommon.js" file, which
contains "createTestMediaPlayer()" function which creates fake
media player with shadow roots for tests to use.

The media player assumed that <input> tag can contain some other
tags like <input type="range"><div>...</div></input>, which is not
true. Usually <input> doesn't require its closing tag, thus
the <div> inside <input> becomes just a sibling of the <input>.

The tests which used crateTestMediaPlayer() depended on the
DOM tree structure with the wrong assumption (given above),
so as a 1st step I replaced the <input> with <div tabindex="0">s
so that we keep the tree structure as is while the element is
clickable.

Now the tree structure looks like:

div#player
  input#outside-control (type=checkbox)
  div#player-shadow-host
    #shadow-root
      div#controls
        button.play_button
        div#timeline (used to be <input type=range>)
          div#timeline-shadow-host
            #shadow-root
              div#timeline-slider-thumb
        div#volue-slider-container
          div#volume-slider (used to be <input type=range>)
            div#volume-shadow-host
              #shadow-root
                div#volume-slider-thumb

On the 2nd step, I fixed the test expectations. These tests
(events/event-dispatch/test-001.html and
events/event-retargeting/test-004.html) relied on the fact that
<input> is implemented using user-agent shadow, thus e.g.
a click event on #volume-slider-thumb, will be retargeted
This is no longer true as all elements inside the whole control
is implemented by plain <div>s, and #timeline and #volume-slider
cannot be a shadow boundary. These expectations are adjusted.

[hoppipolla-critic-bot]

Critic review: https://critic.hoppipolla.co.uk/r/5736

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[TakayoshiKochi]

@hayatoito PTAL