[Modern Media Controls] Media Controller: Placard support

[Modern Media Controls] Media Controller: Placard support
https://bugs.webkit.org/show_bug.cgi?id=163731
<rdar://problem/28869598>

Reviewed by Dean Jackson.

We introduce the PlacardSupport class which brings support for showing the
appropriate placard when the media is played via AirPlay or in picture-in-picture.

Tests: media/modern-media-controls/placard-support/placard-support-airplay.html
       media/modern-media-controls/placard-support/placard-support-pip.html

* Modules/modern-media-controls/js-files:
* Modules/modern-media-controls/media/media-controller.js:
(MediaController):
* Modules/modern-media-controls/media/placard-support.js: Added.
(PlacardSupport):
(PlacardSupport.prototype.get mediaEvents):
(PlacardSupport.prototype.handleEvent):
(PlacardSupport.prototype._updatePlacard):
* WebCore.xcodeproj/project.pbxproj:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@208182 268f45cc-cd09-0410-ab3c-d52691b4dbfc