[GTK][CMake] Generate GObject DOM bindings .symbols files

[GTK][CMake] Generate GObject DOM bindings .symbols files
https://bugs.webkit.org/show_bug.cgi?id=126210

Reviewed by Martin Robinson.

.:

* Source/PlatformGTK.cmake: add checking DOM bindings API as a dependency
for documentation generation.

Source/WebCore:

No new tests. Build change only.

* CMakeLists.txt: list Quota module files and IDLs even if the feature
is disabled, for GTK, since we rely on that for our DOM bindings.
* PlatformGTK.cmake: add a new target to check for DOM symbols API by
running the new python script.
* bindings/gobject/GNUmakefile.am: call the new python script instead
of using a custom rule.

Tools:

* gtk/check-gdom-symbols: Added. Checks symbols compatibility.
(should_update_symbols_file):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@164076 268f45cc-cd09-0410-ab3c-d52691b4dbfc