Rename DataTransferAccessPolicy to match spec and refactor related node

Rename DataTransferAccessPolicy to match spec and refactor related node
https://bugs.webkit.org/show_bug.cgi?id=175704

Reviewed by Wenson Hsieh.

Renamed DataTransferAccessPolicy to DataTransfer::StoreMode to match the drag data store mode concept
in the HTML5 specification:
https://html.spec.whatwg.org/multipage/dnd.html#drag-data-store-mode

DataTransfer in addition to those states can be disassociated from the drag data store when it becomes
no longer valid. We also support a special mode which allows only updating the drag image.
These two states, Invalid and DragImageWritable, are added in addition to the three states in the spec.

Also split DragAndDrop type of DataTransfer into DragAndDropData and DragAndDropFiles, and refactored
the related code.

No new tests since there should be no behavioral change.

* WebCore.xcodeproj/project.pbxproj:
* dom/DataTransfer.cpp:
(WebCore::DataTransfer::DataTransfer): No longer takes forFileDrag boolean since it's folded into type.
(WebCore::DataTransfer::createForCopyAndPaste):
(WebCore::DataTransfer::~DataTransfer):
(WebCore::DataTransfer::setAccessPolicy): Deleted.
(WebCore::DataTransfer::canReadTypes const):
(WebCore::DataTransfer::canReadData const):
(WebCore::DataTransfer::canWriteData const):
(WebCore::DataTransfer::createForInputEvent):
(WebCore::DataTransfer::createForDrag):
(WebCore::DataTransfer::createForDrop):
(WebCore::DataTransfer::canSetDragImage const):
* dom/DataTransfer.h:
(WebCore::DataTransfer::makeInvalidForSecurity): Added.
(WebCore::DataTransfer::makeDragImageWritable): Added.
* dom/DataTransferAccessPolicy.h: Removed.
* editing/Editor.cpp:
(WebCore::dispatchClipboardEvent): Moved and renamed from dispatchCPPEvent. Now computes the store mode
inside the function to match the spec: https://w3c.github.io/clipboard-apis/#fire-a-clipboard-event
(WebCore::Editor::canDHTMLCut):
(WebCore::Editor::canDHTMLCopy):
(WebCore::Editor::canDHTMLPaste):
(WebCore::Editor::tryDHTMLCopy):
(WebCore::Editor::tryDHTMLCut):
(WebCore::Editor::tryDHTMLPaste):
(WebCore::Editor::dispatchCPPEvent): Deleted.
* editing/Editor.h:
* page/DragController.cpp:
(WebCore::createDataTransferToUpdateDrag): Extracted to share code.
(WebCore::DragController::dragExited):
(WebCore::DragController::performDragOperation):
(WebCore::DragController::tryDHTMLDrag):
* page/EventHandler.cpp:
(WebCore::EventHandler::invalidateDataTransfer):
(WebCore::EventHandler::handleDrag):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@220935 268f45cc-cd09-0410-ab3c-d52691b4dbfc