Move Mac-only cursor resources to public/resources/

These resources are used only by the webcursor_mac in Chromium. Ideally,
they would move to the Chromium source tree, but that's currently blocked
on some grit issues. In the meantime, this moves them out of core, where
they certainly don't belong.

This patch marks the end of Source/core/Resources (the last image living there,
deleteButton.png, is unused, though a copy of it lives on under LayoutTests).

R=abarth@chromium.org, abarth
BUG=303964

Review URL: https://codereview.chromium.org/26303003

git-svn-id: svn://svn.chromium.org/blink/trunk@159142 bbb929c8-8fbe-4397-9dbb-9b2b20218538