[Web Animations] Update the API to allow the "auto" composite value

[Web Animations] Update the API to allow the "auto" composite value
https://bugs.webkit.org/show_bug.cgi?id=191300
<rdar://problem/45838373>

Reviewed by Dean Jackson.

The Web Animations API has been changed such that the various "composite" properties are no longer optional and instead
allow an "auto" value in their enumeration.

* CMakeLists.txt:
* DerivedSources.make:
* Sources.txt:
* WebCore.xcodeproj/project.pbxproj:
* animation/CompositeOperationOrAuto.h: Copied from Source/WebCore/animation/KeyframeEffect.idl.
* animation/CompositeOperationOrAuto.idl: Copied from Source/WebCore/animation/KeyframeEffect.idl.
* animation/KeyframeEffect.cpp:
(WebCore::processKeyframeLikeObject):
(WebCore::processIterableKeyframes):
(WebCore::processPropertyIndexedKeyframes):
(WebCore::KeyframeEffect::getKeyframes):
* animation/KeyframeEffect.h:
* animation/KeyframeEffect.idl:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@237855 268f45cc-cd09-0410-ab3c-d52691b4dbfc