Rename GN public variables.

forward_dependent_configs_from => public_deps
direct_dependent_configs => public_configs

TBR=jamesr

Review URL: https://codereview.chromium.org/601803003

git-svn-id: svn://svn.chromium.org/blink/trunk@182624 bbb929c8-8fbe-4397-9dbb-9b2b20218538