Apply std::unique_ptr to FooFont classes

Apply std::unique_ptr to FooFont classes
https://bugs.webkit.org/show_bug.cgi?id=137769

Reviewed by Andreas Kling.

As a step to use std::unique_ptr, this patch applies std::unique_ptr to Font classes.

No new tests, no behavior changes.

* platform/graphics/Font.cpp:
(WebCore::retrieveOrAddCachedFontGlyphs):
(WebCore::Font::createLayout):
* platform/graphics/SimpleFontData.cpp:
(WebCore::SimpleFontData::DerivedFontData::create):
* platform/graphics/SimpleFontData.h:
Remove create() factory function because public ctor and std::make_unique<> can replace it.
* platform/graphics/mac/ComplexTextController.cpp:
(WebCore::Font::createLayout):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@174858 268f45cc-cd09-0410-ab3c-d52691b4dbfc