[LFC] Implement Display::Box functions

[LFC] Implement Display::Box functions
https://bugs.webkit.org/show_bug.cgi?id=185116

Reviewed by Antti Koivisto.

* layout/displaytree/DisplayBox.cpp:
(WebCore::Display::Box::Box):
(WebCore::Display::Box::~Box):
(WebCore::Display::Box::marginBox const):
(WebCore::Display::Box::borderBox const):
(WebCore::Display::Box::paddingBox const):
(WebCore::Display::Box::contentBox const):
* layout/displaytree/DisplayBox.h:
(WebCore::Display::Box::rect const):
(WebCore::Display::Box::top const):
(WebCore::Display::Box::left const):
(WebCore::Display::Box::bottom const):
(WebCore::Display::Box::right const):
(WebCore::Display::Box::topLeft const):
(WebCore::Display::Box::bottomRight const):
(WebCore::Display::Box::size const):
(WebCore::Display::Box::width const):
(WebCore::Display::Box::height const):
(WebCore::Display::Box::marginTop const):
(WebCore::Display::Box::marginLeft const):
(WebCore::Display::Box::marginBottom const):
(WebCore::Display::Box::marginRight const):
(WebCore::Display::Box::parent const):
(WebCore::Display::Box::nextSibling const):
(WebCore::Display::Box::previousSibling const):
(WebCore::Display::Box::firstChild const):
(WebCore::Display::Box::lastChild const):
(WebCore::Display::Box::setRect):
(WebCore::Display::Box::setTopLeft):
(WebCore::Display::Box::setTop):
(WebCore::Display::Box::setLeft):
(WebCore::Display::Box::setSize):
(WebCore::Display::Box::setWidth):
(WebCore::Display::Box::setHeight):
(WebCore::Display::Box::setMarginTop):
(WebCore::Display::Box::setMarginLeft):
(WebCore::Display::Box::setMarginBottom):
(WebCore::Display::Box::setMarginRight):
(WebCore::Display::Box::setBorderTop):
(WebCore::Display::Box::setBorderLeft):
(WebCore::Display::Box::setBorderBottom):
(WebCore::Display::Box::setBorderRight):
(WebCore::Display::Box::setPaddingTop):
(WebCore::Display::Box::setPaddingLeft):
(WebCore::Display::Box::setPaddingBottom):
(WebCore::Display::Box::setPaddingRight):
(WebCore::Display::Box::setParent):
(WebCore::Display::Box::setNextSibling):
(WebCore::Display::Box::setPreviousSibling):
(WebCore::Display::Box::setFirstChild):
(WebCore::Display::Box::setLastChild):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@231150 268f45cc-cd09-0410-ab3c-d52691b4dbfc