Move Custom Filter files (with no dependencies on core) from core/... to platform/...

To make the move, I had to had to make a few changes:
(1) Add cpp files for previously header-only classes, so they would be compiled in the platform DLL and available to the core DLL. Those include CustomFilterProgramClient, CustomFilterArrayParameter, and CustomFilterNumberParameter.

(2) Don't use wtf::Vector as a base class for CustomFilterParameterList to make it easier to export. Instead, add a wtf::Vector member to CustomFilterParameterList and forwarding functions for at(), size(), append(), sortParametersByName().

(3) Make CustomFilterParameterList::checkAlphabeticalOrder private and behind NDEBUG because it's only used in asserts. Remove a call to it from CustomFilterOperation::CustomFilterOperation, since the asserts in CustomFilterParameterList::blend are sufficient.

(4) Change the name of some constants from UNDERSCORES_AND_CAPS to CamelCase to pass new style rules.

BUG=303332

Review URL: https://codereview.chromium.org/45873002

git-svn-id: svn://svn.chromium.org/blink/trunk@161097 bbb929c8-8fbe-4397-9dbb-9b2b20218538