[WPE] Add gtk-doc

[WPE] Add gtk-doc
https://bugs.webkit.org/show_bug.cgi?id=178900

Patch by Carlos Eduardo Ramalho <cadubentzen@gmail.com> on 2018-12-04
Reviewed by Michael Catanzaro.

Add gtk-doc to WPE port. This patch tries to reuse as much code from
WebKitGTK+ as possible.

.:

* Source/PlatformGTK.cmake: include GtkDoc.cmake instead of defining macro.
* Source/PlatformWPE.cmake: Added documentation generation.
* Source/cmake/GtkDoc.cmake: Added.
* Source/cmake/OptionsWPE.cmake: Added ENABLE_GTKDOC build option and added pkg-config path variables.

Source/WebKit:

* PlatformWPE.cmake: Write variables to gtkdoc-wpe.cfg and gtkdoc-webextensions that is used by python script later.
* UIProcess/API/wpe/WebKitWebContext.h: Placed sandbox functions in the same location as in the WebKitGTK+ for consistency.
* UIProcess/API/wpe/docs/wpe-0.1-sections.txt: Added.
* UIProcess/API/wpe/docs/wpe-docs.sgml: Added.
* WebProcess/InjectedBundle/API/wpe/WebKitWebPage.h: Placed webkit_web_page_get_dom_document
in the same position as in the WebKitGTK+ for consistency.
* WebProcess/InjectedBundle/API/wpe/docs/wpe-webextensions-0.1-sections.txt: Added.
* WebProcess/InjectedBundle/API/wpe/docs/wpe-webextensions-docs.sgml: Added.

Tools:

* gtkdoc/generate-gtkdoc: Renamed from Tools/gtk/generate-gtkdoc.
(get_gtkdoc_module_paths): Add GDK and GTK only if building for GTK.
(prepare_environment_for_gtkdoc_generation):
(build_gtkdoc_for_wpe): Code to generate doc for WPE.
(build_gtkdoc_for_wkgtk): Code to generate doc for WebKitGTK+. Moved from main.
* gtkdoc/gtkdoc.py: Renamed from Tools/gtk/gtkdoc.py.
(GTKDoc.__init__): Initialized required variables according to pylint.
(GTKDoc.api_missing_documentation):
* wpe/install-dependencies: Add gtkdoc dependency.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@238853 268f45cc-cd09-0410-ab3c-d52691b4dbfc